1 lvalue required as left operand of assignment

Solve error: lvalue required as left operand of assignment

In this tutorial you will know about one of the most occurred error in C and C++ programming, i.e. lvalue required as left operand of assignment.

lvalue means left side value. Particularly it is left side value of an assignment operator.

rvalue means right side value. Particularly it is right side value or expression of an assignment operator.

In above example a is lvalue and b + 5 is rvalue.

In C language lvalue appears mainly at four cases as mentioned below:

Left of assignment operator.
Left of member access (dot) operator (for structure and unions).
Right of address-of operator (except for register and bit field lvalue).
As operand to pre/post increment or decrement for integer lvalues including Boolean and enums.

Now let see some cases where this error occur with code.

When you will try to run above code, you will get following error.

Solution: In if condition change assignment operator to comparison operator, as shown below.

Above code will show the error: lvalue required as left operand of assignment operator.

Here problem occurred due to wrong handling of short hand operator (*=) in findFact() function.

Solution : Just by changing the line ans*i=ans to ans*=i we can avoid that error. Here short hand operator expands like this, ans=ans*i. Here left side some variable is there to store result. But in our program ans*i is at left hand side. It’s an expression which produces some result. While using assignment operator we can’t use an expression as lvalue.

The correct code is shown below.

Above code will show the same lvalue required error.

Reason and Solution: Ternary operator produces some result, it never assign values inside operation. It is same as a function which has return type. So there should be something to be assigned but unlike inside operator.

The correct code is given below.

Some Precautions To Avoid This Error

There are no particular precautions for this. Just look into your code where problem occurred, like some above cases and modify the code according to that.

Mostly 90% of this error occurs when we do mistake in comparison and assignment operations. When using pointers also we should careful about this error. And there are some rare reasons like short hand operators and ternary operators like above mentioned. We can easily rectify this error by finding the line number in compiler, where it shows error: lvalue required as left operand of assignment.

Programming Assignment Help on Assigncode.com, that provides homework ecxellence in every technical assignment.

Comment below if you have any queries related to above tutorial.

Basic structure of c program, introduction to c programming language, variables, constants and keywords in c, first c program – print hello world message, 6 thoughts on “solve error: lvalue required as left operand of assignment”.

hi sir , i am andalib can you plz send compiler of c++.

i want the solution by char data type for this error

#include #include #include using namespace std; #define pi 3.14 int main() { float a; float r=4.5,h=1.5; {

a=2*pi*r*h=1.5 + 2*pi*pow(r,2); } cout<<" area="<<a<<endl; return 0; } what's the problem over here

#include using namespace std; #define pi 3.14 int main() { float a,p; float r=4.5,h=1.5; p=2*pi*r*h; a=1.5 + 2*pi*pow(r,2);

cout<<" area="<<a<<endl; cout<<" perimeter="<<p<<endl; return 0; }

You can't assign two values at a single place. Instead solve them differetly

Hi. I am trying to get a double as a string as efficiently as possible. I get that error for the final line on this code. double x = 145.6; int size = sizeof(x); char str[size]; &str = &x; Is there a possible way of getting the string pointing at the same part of the RAM as the double?

【C】报错[Error] lvalue required as left operand of assignment

1 lvalue required as left operand of assignment

[Error] lvalue required as left operand of assignment

计算值为== ！=

赋值语句的左边应该是变量，不能是表达式。而实际上，这里是一个比较表达式，所以要把赋值号（＝）改用关系运算符（＝＝）

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How To Fix “error: lvalue required as left operand of assignment”

The message “error: lvalue required as left operand of assignment” can be shown quite frequently when you write your C/C++ programs. Check out the explanation below to understand why it happens.

Table of Contents

l-values And r-values

In C and C++, we can put expressions into many categories , including l-values and r-values

The history of these concepts can be traced back to Combined Programming Language. Their names are derived from the sides where they are typically located on an assignment statement.

Recent standards like C++17 actually define several categories like xvalue or prvalue. But the definitions of l-values and r-values are basically the same in all C and C++ standards.

In simple terms, l-values are memory addresses that C/C++ programs can access programmatically. Common examples include constants, variable names, class members, unions, bit-fields, and array elements.

In an assignment statement, the operand on the left-hand side should be a modifiable l-value because the operator will evaluate the right operand and assign its result to the left operand.

This example illustrates the common correct usage of l-values and r-values:

In the ‘x = 4’ statement, x is an l-value while the literal 4 is not. The increment operator also requires an l-value because it needs to read the operand value and modify it accordingly.

Similarly, dereferenced pointers like *p are also l-values. Notice that an l-value (like x) can be on the right side of the assignment statement as well.

Causes And Solutions For “error: lvalue required as left operand of assignment”

C/C++ compilers generates this error when you don’t provide a valid l-value to the left-hand side operand of an assignment statement. There are many cases you can make this mistake.

This code can’t be compiled successfully:

As we have mentioned, the number literal 4 isn’t an l-value, which is required for the left operand. You will need to write the assignment statement the other way around:

In the same manner, this program won’t compile either:

In C/C++, the ‘x + 1’ expression doesn’t evaluate to a l-value. You can fix it by switching the sides of the operands:

This is another scenario the compiler will complain about the left operand:

(-x) doesn’t evaluate to a l-value in C/C++, while ‘x’ does. You will need to change both operands to make the statement correct:

Many people also use an assignment operator when they need a comparison operator instead:

This leads to a compilation error:

The if statement above needs to check the output of a comparison statement:

if (strcmp (str1,str2) == 0)

C/C++ compilers will give you the message “ error: lvalue required as left operand of assignment ” when there is an assignment statement in which the left operand isn’t a modifiable l-value. This is usually the result of syntax misuse. Correct it, and the error should disappear.

Maybe you are interested :

Expression preceding parentheses of apparent call must have (pointer-to-) function type
ERROR: conditional jump or move depends on the uninitialized value(s)
Print a vector in C++

My name is Robert. I have a degree in information technology and two years of expertise in software development. I’ve come to offer my understanding on programming languages. I hope you find my articles interesting.

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Understanding the Meaning and Solutions for 'lvalue Required as Left Operand of Assignment'

If you are a developer who has encountered the error message 'lvalue required as left operand of assignment' while coding, you are not alone. This error message can be frustrating and confusing for many developers, especially those who are new to programming. In this guide, we will explain what this error message means and provide solutions to help you resolve it.

What Does 'lvalue Required as Left Operand of Assignment' Mean?

The error message "lvalue required as left operand of assignment" typically occurs when you try to assign a value to a constant or an expression that cannot be assigned a value. An lvalue is a term used in programming to refer to a value that can appear on the left side of an assignment operator, such as "=".

For example, consider the following line of code:

In this case, the value "5" cannot be assigned to the variable "x" because "5" is not an lvalue. This will result in the error message "lvalue required as left operand of assignment."

Solutions for 'lvalue Required as Left Operand of Assignment'

If you encounter the error message "lvalue required as left operand of assignment," there are several solutions you can try:

Solution 1: Check Your Assignments

The first step you should take is to check your assignments and make sure that you are not trying to assign a value to a constant or an expression that cannot be assigned a value. If you have made an error in your code, correcting it may resolve the issue.

Solution 2: Use a Pointer

If you are trying to assign a value to a constant, you can use a pointer instead. A pointer is a variable that stores the memory address of another variable. By using a pointer, you can indirectly modify the value of a constant.

Here is an example of how to use a pointer:

In this case, we create a pointer "ptr" that points to the address of "x." We then use the pointer to indirectly modify the value of "x" by assigning it a new value of "10."

Solution 3: Use a Reference

Another solution is to use a reference instead of a constant. A reference is similar to a pointer, but it is a direct alias to the variable it refers to. By using a reference, you can modify the value of a variable directly.

Here is an example of how to use a reference:

In this case, we create a reference "ref" that refers to the variable "x." We then use the reference to directly modify the value of "x" by assigning it a new value of "10."

Q1: What does the error message "lvalue required as left operand of assignment" mean?

A1: This error message typically occurs when you try to assign a value to a constant or an expression that cannot be assigned a value.

Q2: How can I resolve the error message "lvalue required as left operand of assignment?"

A2: You can try checking your assignments, using a pointer, or using a reference.

Q3: Can I modify the value of a constant?

A3: No, you cannot modify the value of a constant directly. However, you can use a pointer to indirectly modify the value.

Q4: What is an lvalue?

A4: An lvalue is a term used in programming to refer to a value that can appear on the left side of an assignment operator.

Q5: What is a pointer?

A5: A pointer is a variable that stores the memory address of another variable. By using a pointer, you can indirectly modify the value of a variable.

In conclusion, the error message "lvalue required as left operand of assignment" can be frustrating for developers, but it is a common error that can be resolved using the solutions we have provided in this guide. By understanding the meaning of the error message and using the appropriate solution, you can resolve this error and continue coding with confidence.

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Understanding lvalues and rvalues in C and C++

The terms lvalue and rvalue are not something one runs into often in C/C++ programming, but when one does, it's usually not immediately clear what they mean. The most common place to run into these terms are in compiler error & warning messages. For example, compiling the following with gcc :

True, this code is somewhat perverse and not something you'd write, but the error message mentions lvalue , which is not a term one usually finds in C/C++ tutorials. Another example is compiling this code with g++ :

Now the error is:

Here again, the error mentions some mysterious rvalue . So what do lvalue and rvalue mean in C and C++? This is what I intend to explore in this article.

A simple definition

This section presents an intentionally simplified definition of lvalues and rvalues . The rest of the article will elaborate on this definition.

An lvalue ( locator value ) represents an object that occupies some identifiable location in memory (i.e. has an address).

rvalues are defined by exclusion, by saying that every expression is either an lvalue or an rvalue . Therefore, from the above definition of lvalue , an rvalue is an expression that does not represent an object occupying some identifiable location in memory.

Basic examples

The terms as defined above may appear vague, which is why it's important to see some simple examples right away.

Let's assume we have an integer variable defined and assigned to:

An assignment expects an lvalue as its left operand, and var is an lvalue, because it is an object with an identifiable memory location. On the other hand, the following are invalid:

Neither the constant 4 , nor the expression var + 1 are lvalues (which makes them rvalues). They're not lvalues because both are temporary results of expressions, which don't have an identifiable memory location (i.e. they can just reside in some temporary register for the duration of the computation). Therefore, assigning to them makes no semantic sense - there's nowhere to assign to.

So it should now be clear what the error message in the first code snippet means. foo returns a temporary value which is an rvalue. Attempting to assign to it is an error, so when seeing foo() = 2; the compiler complains that it expected to see an lvalue on the left-hand-side of the assignment statement.

Not all assignments to results of function calls are invalid, however. For example, C++ references make this possible:

Here foo returns a reference, which is an lvalue , so it can be assigned to. Actually, the ability of C++ to return lvalues from functions is important for implementing some overloaded operators. One common example is overloading the brackets operator [] in classes that implement some kind of lookup access. std::map does this:

The assignment mymap[10] works because the non-const overload of std::map::operator[] returns a reference that can be assigned to.

Modifiable lvalues

Initially when lvalues were defined for C, it literally meant "values suitable for left-hand-side of assignment". Later, however, when ISO C added the const keyword, this definition had to be refined. After all:

So a further refinement had to be added. Not all lvalues can be assigned to. Those that can are called modifiable lvalues . Formally, the C99 standard defines modifiable lvalues as:

[...] an lvalue that does not have array type, does not have an incomplete type, does not have a const-qualified type, and if it is a structure or union, does not have any member (including, recursively, any member or element of all contained aggregates or unions) with a const-qualified type.

Conversions between lvalues and rvalues

Generally speaking, language constructs operating on object values require rvalues as arguments. For example, the binary addition operator '+' takes two rvalues as arguments and returns an rvalue:

As we've seen earlier, a and b are both lvalues. Therefore, in the third line, they undergo an implicit lvalue-to-rvalue conversion . All lvalues that aren't arrays, functions or of incomplete types can be converted thus to rvalues.

What about the other direction? Can rvalues be converted to lvalues? Of course not! This would violate the very nature of an lvalue according to its definition [1] .

This doesn't mean that lvalues can't be produced from rvalues by more explicit means. For example, the unary '*' (dereference) operator takes an rvalue argument but produces an lvalue as a result. Consider this valid code:

Conversely, the unary address-of operator '&' takes an lvalue argument and produces an rvalue:

The ampersand plays another role in C++ - it allows to define reference types. These are called "lvalue references". Non-const lvalue references cannot be assigned rvalues, since that would require an invalid rvalue-to-lvalue conversion:

Constant lvalue references can be assigned rvalues. Since they're constant, the value can't be modified through the reference and hence there's no problem of modifying an rvalue. This makes possible the very common C++ idiom of accepting values by constant references into functions, which avoids unnecessary copying and construction of temporary objects.

CV-qualified rvalues

If we read carefully the portion of the C++ standard discussing lvalue-to-rvalue conversions [2] , we notice it says:

An lvalue (3.10) of a non-function, non-array type T can be converted to an rvalue. [...] If T is a non-class type, the type of the rvalue is the cv-unqualified version of T. Otherwise, the type of the rvalue is T.

What is this "cv-unqualified" thing? CV-qualifier is a term used to describe const and volatile type qualifiers.

From section 3.9.3:

Each type which is a cv-unqualified complete or incomplete object type or is void (3.9) has three corresponding cv-qualified versions of its type: a const-qualified version, a volatile-qualified version, and a const-volatile-qualified version. [...] The cv-qualified or cv-unqualified versions of a type are distinct types; however, they shall have the same representation and alignment requirements (3.9)

But what has this got to do with rvalues? Well, in C, rvalues never have cv-qualified types. Only lvalues do. In C++, on the other hand, class rvalues can have cv-qualified types, but built-in types (like int ) can't. Consider this example:

The second call in main actually calls the foo () const method of A , because the type returned by cbar is const A , which is distinct from A . This is exactly what's meant by the last sentence in the quote mentioned earlier. Note also that the return value from cbar is an rvalue. So this is an example of a cv-qualified rvalue in action.

Rvalue references (C++11)

Rvalue references and the related concept of move semantics is one of the most powerful new features the C++11 standard introduces to the language. A full discussion of the feature is way beyond the scope of this humble article [3] , but I still want to provide a simple example, because I think it's a good place to demonstrate how an understanding of what lvalues and rvalues are aids our ability to reason about non-trivial language concepts.

I've just spent a good part of this article explaining that one of the main differences between lvalues and rvalues is that lvalues can be modified, and rvalues can't. Well, C++11 adds a crucial twist to this distinction, by allowing us to have references to rvalues and thus modify them, in some special circumstances.

As an example, consider a simplistic implementation of a dynamic "integer vector". I'm showing just the relevant methods here:

So, we have the usual constructor, destructor, copy constructor and copy assignment operator [4] defined, all using a logging function to let us know when they're actually called.

Let's run some simple code, which copies the contents of v1 into v2 :

What this prints is:

Makes sense - this faithfully represents what's going on inside operator= . But suppose that we want to assign some rvalue to v2 :

Although here I just assign a freshly constructed vector, it's just a demonstration of a more general case where some temporary rvalue is being built and then assigned to v2 (this can happen for some function returning a vector, for example). What gets printed now is this:

Ouch, this looks like a lot of work. In particular, it has one extra pair of constructor/destructor calls to create and then destroy the temporary object. And this is a shame, because inside the copy assignment operator, another temporary copy is being created and destroyed. That's extra work, for nothing.

Well, no more. C++11 gives us rvalue references with which we can implement "move semantics", and in particular a "move assignment operator" [5] . Let's add another operator= to Intvec :

The && syntax is the new rvalue reference . It does exactly what it sounds it does - gives us a reference to an rvalue, which is going to be destroyed after the call. We can use this fact to just "steal" the internals of the rvalue - it won't need them anyway! This prints:

What happens here is that our new move assignment operator is invoked since an rvalue gets assigned to v2 . The constructor and destructor calls are still needed for the temporary object that's created by Intvec(33) , but another temporary inside the assignment operator is no longer needed. The operator simply switches the rvalue's internal buffer with its own, arranging it so the rvalue's destructor will release our object's own buffer, which is no longer used. Neat.

I'll just mention once again that this example is only the tip of the iceberg on move semantics and rvalue references. As you can probably guess, it's a complex subject with a lot of special cases and gotchas to consider. My point here was to demonstrate a very interesting application of the difference between lvalues and rvalues in C++. The compiler obviously knows when some entity is an rvalue, and can arrange to invoke the correct constructor at compile time.

One can write a lot of C++ code without being concerned with the issue of rvalues vs. lvalues, dismissing them as weird compiler jargon in certain error messages. However, as this article aimed to show, getting a better grasp of this topic can aid in a deeper understanding of certain C++ code constructs, and make parts of the C++ spec and discussions between language experts more intelligible.

Also, in the new C++ spec this topic becomes even more important, because C++11's introduction of rvalue references and move semantics. To really grok this new feature of the language, a solid understanding of what rvalues and lvalues are becomes crucial.

For comments, please send me an email .

Lvalue Required as Left Operand of Assignment: Effective Solutions

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How to fix error lvalue required as left operand of assignment

Keep on reading this guide as our experts teach you the different scenarios that can cause this error and how you can fix it. In addition, we’ll also answer some commonly-asked questions about the lvalue required error.

JUMP TO TOPIC

– Misuse of the Assignment Operator

– mishandling of the multiplication assignment operator, – misunderstanding the ternary operator, – using pre-increment on a temporary variable, – direct decrement of a numeric literal, – using a pointer to a variable value, – wrong placement of expression, – use equality operator during comparisons, – use a counter variable as the value of the multiplication assignment operator, – use the ternary operator the right way, – don’t pre-increment a temporary variable, – use pointer on a variable, not its value, – place an expression on the right side, – what is meant by left operand of assignment, – what is lvalues and rvalues, – what is lvalue in arduino, why do you have the error lvalue required as left operand of assignment.

The reason you are seeing the lvalue required error is because of several reasons such as: misuse of the assignment operator, mishandling of the multiplication assignment operator, misunderstanding the ternary operator, or using pre-increment on a temporary variable. Direct decrement of a numeric literal, using a pointer to a numeric value, and wrong placement of expression can also cause this error.

The first step to take after receiving such an error is to diagnose the root cause of the problem. As you can see, there are a lot of possible causes as to why this is occurring, so we’ll take a closer look at all of them to see which one fits your experience.

When you misuse the equal sign in your code, you’ll run into the lvalue required error. This occurs when you are trying to check the equality of two variables , so during the check, you might have used the equal sign instead of an equality check. As a result, when you compile the code, you’ll get the lvalue required error.

In the C code below, we aim to check for equality between zero and the result of the remainder between 26 and 13. However, in the check, we used the equal sign on the left hand of the statement. As a result, we get an error when we compare it with the right hand operand.

Mishandling of the multiplication assignment operator will result in the lvalue required error. This happens if you don’t know how compilers evaluate a multiplication assignment operator. For example, you could write your statement using the following format:

variable * increment = variable

The format of this statement will cause an error because the left side is an expression, and you cannot use an expression as an lvalue. This is synonymous to 20 multiplied by 20 is equal to 20, so the code below is an assignment error.

The ternary operator produces a result, it does not assign a value. So an attempt to assign a value will result in an error . Observe the following ternary operator:

(x>y)?y=x:y=y

Many compilers will parse this as the following:

((x>y)?y=x:y)=y

This is an error. That is because the initial ternary operator ((x>y)?y=x:y) results in an expression. That’s what we’ve done in the next code block. As a result, it leads to the error lvalue required as left operand of assignment ternary operator.

An attempt to pre-increment a temporary variable will also lead to an lvalue required error. That is because a temporary variable has a short lifespan , so they tend to hold data that you’ll soon discard. Therefore, trying to increment such a variable will lead to an error.

For example, in the code below, we pre-increment a variable after we decrement it. As a result, it leads to the error lvalue required as increment operand.

Direct decrement of a numeric literal will lead to an error . That is because in programming, it’s illegal to decrement a numeric literal, so don’t do it, use variables instead. We’ll show you a code example so you’ll know what to avoid in your code.

In our next code block, we aim to reduce the value of X and Y variables. However, decrementing the variables directly leads to error lvalue required as decrement operand . That’s because the direct decrement is illegal, so, it’s an assignment error.

An attempt to use a pointer on a variable value will lead to lvalue required error. That’s because the purpose of the pointer sign (&) is to refer to the address of a variable, not the value of the variable.

In the code below, we’ve used the pointer sign (&) on the value of the Z variable. As a result, when you compile the code you get the error lvalue required as unary ‘&’ operand.

If you place an expression in the wrong place, it’ll lead to an error lvalue required as operand. It gets confusing if you assign the expression to a variable used in the expression. Therefore, this can result in you assigning the variable to itself.

The following C++ code example will result in an error. That is because we’ve incremented the variable and we assign it to itself.

How To Fix Lvalue Required as Left Operand of Assignment

Now that you know what is causing this error to appear, it’s now time to take actionable steps to fix the problem . In this section, we’ll be discussing these solutions in more detail.

During comparisons, use the equality operator after the left operand . By doing this, you’ve made it clear to the compiler that you are doing comparisons, so this will prevent an error.

The following code is the correct version of the first example in the code. We’ve added a comment to the corrected code so you can observe the difference.

When doing computation with the multiplication assignment operator (*=), use the counter variable. Do not use another variable that can lead to an error. For example, in the code below, we’ve made changes to the second example in this article. This shows you how to prevent the error.

Use the ternary operator without assuming what should happen . Be explicit and use the values that will allow the ternary operator to evaluate. We present an example below.

That’s right, do not pre-increment a temporary variable . That’s because they only serve a temporary purpose.

At one point in this article, we showed you a code example where we use a pre-increment on a temporary variable. However, in the code below, we rewrote the code to prevent the error.

The job of a pointer is to point to a variable location in memory, so you can make an assumption that using the variable value should work. However, it won’t work , as we’ve shown you earlier in the guide.

In the code below, we’ve placed the pointer sign (&) between the left operand and the right operand.

When you place an expression in place of the left operand, you’ll receive an error, so it’s best to place the expression on the right side. Meanwhile, on the right, you can place the variable that gets the result of the expression.

In the following code, we have an example from earlier in the article. However, we’ve moved the expression to the right where it occupied the left operand position before.

Lvalue Required: Common Questions Answered

In this section, we’ll answer questions related to the lvalue error and we’ll aim to clear further doubts you have about this error.

The left operand meaning is as follows: a modifiable value that is on the left side of an expression.

An lvalue is a variable or an object that you can use after an expression , while an rvalue is a temporary value. As a result, once the expression is done with it, it does not persist afterward.

Lvalue in Arduino is the same as value in C , because you can use the C programming language in Arduino. However, misuse or an error could produce an error that reads error: lvalue required as left operand of assignment #define high 0x1.

What’s more, Communication Access Programming Language (CAPL) will not allow the wrong use of an lvalue . As a result, any misuse will lead to the left value required capl error. As a final note, when doing network programming in C, be wary of casting a left operand as this could lead to lvalue required as left operand of assignment struct error.

This article explained the different situations that will cause an lvalue error, and we also learned about the steps we can take to fix it . We covered a lot, and the following are the main points you should hold on to:

A misuse of the assignment operator will lead to a lvalue error, and using the equality operator after the left operand will fix this issue.
Using a pointer on the variable instead of the value will prevent the lvalue assignment error.
A pre-increment on a temporary variable will cause the lvalue error. Do not pre-increment on a temporary variable to fix this error.
An lvalue is a variable while an rvalue is a temporary variable.
Place an expression in the right position to prevent an lvalue error, as the wrong placement of expressions can also cause this error to appear.

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Understanding and Resolving the 'lvalue Required: Left Operand Assignment' Error in C++

Abstract: In C++ programming, the 'lvalue Required: Left Operator Assignment' error occurs when assigning a value to an rvalue. In this article, we'll discuss the error in detail, provide examples, and discuss possible solutions.

Understanding and Resolving the "lvalue Required Left Operand Assignment" Error in C++

In C++ programming, one of the most common errors that beginners encounter is the "lvalue required as left operand of assignment" error. This error occurs when the programmer tries to assign a value to an rvalue, which is not allowed in C++. In this article, we will discuss the concept of lvalues and rvalues, the causes of this error, and how to resolve it.

Lvalues and Rvalues

In C++, expressions can be classified as lvalues or rvalues. An lvalue (short for "left-value") is an expression that refers to a memory location and can appear on the left side of an assignment. An rvalue (short for "right-value") is an expression that does not refer to a memory location and cannot appear on the left side of an assignment.

For example, consider the following code:

In this code, x is an lvalue because it refers to a memory location that stores the value 5. The expression x = 10 is also an lvalue because it assigns the value 10 to the memory location referred to by x . However, the expression 5 is an rvalue because it does not refer to a memory location.

Causes of the Error

The "lvalue required as left operand of assignment" error occurs when the programmer tries to assign a value to an rvalue. This is not allowed in C++ because rvalues do not have a memory location that can be modified. Here are some examples of code that would cause this error:

In each of these examples, the programmer is trying to assign a value to an rvalue, which is not allowed. The error message indicates that an lvalue is required as the left operand of the assignment operator ( = ).

Resolving the Error

To resolve the "lvalue required as left operand of assignment" error, the programmer must ensure that the left operand of the assignment operator is an lvalue. Here are some examples of how to fix the code that we saw earlier:

In each of these examples, we have ensured that the left operand of the assignment operator is an lvalue. This resolves the error and allows the program to compile and run correctly.

The "lvalue required as left operand of assignment" error is a common mistake that beginners make when learning C++. To avoid this error, it is important to understand the difference between lvalues and rvalues and to ensure that the left operand of the assignment operator is always an lvalue. By following these guidelines, you can write correct and efficient C++ code.

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"lvalue required as left operand of assignment" on cppreference.com

Learn how to resolve 'lvalue Required: Left Operand Assignment' error in C++ by understanding the concept of lvalues and rvalues and applying the appropriate solutions.

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Tags: : C++ Programming Error Debugging

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Lvalue Required as Left Operand of Assignment

Let us understand all about the error lvalue required as left operand of assignment in C programming language.

We will also showcase an implementation of lvalue and rvalue in C programming. This guide will help you in understanding how to remove lvalue required error in Turbo C, C++, Codeblocks, GCC and other compilers.

The lvalue required as left operand of assignment error occurs irrespective of the programming language because it is the basic syntax of writing an expression.

What is an Expression?

An expression is a valid and well-defined unit of code that resolves to a resultant value which is measurable. This expression can be a mathematical expression that can be evaluated to a value.

This expression can be a combination of constants, numerical values, variables, functions, operators and all these are evaluated to result into an operand.

Any expression is a combination of operators and operands. An operand could be a value, variable, constants, etc.

Must Read: C Programs For Numerical Methods

There are different types of C operators such as:

Relational operators
Assignment operators
Arithmetic operators
Bitwise operators
Increment/decrement operators
Special operators
Logical operators

Let us see an example of a mathematical expression here.

A mathematical expression, or any generic expression for that matter, contains two parts viz. lvalue and rvalue.

What is Lvalue?

The lvalue represents the left value in an expression which is the left-hand portion of an expression. So, it is essentially the evaluated result.

If you try to compare it with the above expression example, r is the lvalue which is assigned the result of the right-hand portion.

What is Rvalue?

As you might have guessed it by now, the rvalue represents the right value in an expression which is the right-hand portion of an expression.

This rvalue is the part of the expression that gets computed and assigned to the lvalue of the expression. In this case, it is 4x + 3y + z .

What is lvalue required as left operand of assignment error?

The Left operand of assignment has something to do with the left-hand side of the assignment operator which is the = operator.

Generally, any computation is performed on the right-hand side of the expression and the evaluated result is stored in left-hand side.

This error occurs when you try to reverse the way how an expression is evaluated.

If you try to perform something like above expression, then it could have two possible meaning:

The value of c should be stored in 3a + 2b which is not possible and does not make sense either.
The value of 3a + 2b should be stored in c which goes against the rule of assignment in an expression.

Normally, the assignment operator ( equal to operator in this case) assigns the result from right-hand side to left-hand side.

So the above mathematical expression in any programming language will definitely throw the lvalue required error in c programming .

Let us see an example below that generates this error in C programming language.

Note: The following C programming code is compiled with GNU GCC compiler on CodeLite IDE in Windows 10 operating system. However, these codes are compatible with all other operating systems.

Example: Error lvalue required as left operand of assignment GCC Compiler

error lvalue required as left operand of assignment gcc compiler output

To solve the above error, all you need to do is to reverse the expression. Ensure c should be on LHS and 2*x + 3*y should be on RHS .

The evaluation or the calculation with operators, variables, operands, constants should always be on RHS and it is just the calculated result that should be equated on the right-hand side.

To solve the above lvalue error in C programming, please refer to the following code.

One common mistake that programmers often commit is that they tend to use comparison operator == instead of assignment operator = .

Must Read: C Program For Hexadecimal To Binary Conversion

Lvalue Error Examples and Solutions

Error 1: String Comparison

Here, we are trying to compare the strings. However, we have used the = operator which is an assignment and not a comparison operator. Hence, it shall give us the lvalue required error .

Error 2: Variable Comparison

Here you are trying to compare the variable a with a constant value of 5. However, the assignment operator is used instead of the comparison operator and as a result, it will display the error: lvalue required as left operand of assignment .

Let’s discuss more on the error lvalue required as left operand of assignment in the comment section below if you have any compilation errors and any doubts about the same. For more information check Wikipedia .

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3 thoughts on “ Lvalue Required as Left Operand of Assignment ”

Thank you so much. I could finally resolve lvalue error in Turbo C software.

I am using Turbo C software for my C programming and I used to get the Lvalue required error in Turbo C very usually. Thanks for this one.

Lvalue Error Examples and Solutions :

2) if(r=5) { }.its working correctly . But if u write as: if(5=r) { }.then it will shown lvalue required error. and if u write like if(5==r) { }.then it will shown output.

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10 4 C:\Users\30950\Desktop\调试\C语言\test-C++.cpp [Error] lvalue required as increment operand

6 11 c:\users\27710\desktop\dev-c++\3.cpp [error] lvalue required as decrement operand, 11 11 c:\users\27710\desktop\dev-c++\2.cpp [error] lvalue required as left operand of assignment.

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lvalue required as left operand of assignment PLEASE HELP ME!

Please help me AS SOON AS POSSIBLE! I have a projekt and i have the message: lvalue required as left operand of assignment

More informations: Arduino: 1.6.7 (Windows 8.1), Board: "Arduino/Genuino Mega or Mega 2560, ATmega2560 (Mega 2560)"

In function 'void setup()':

Vorw_rtsfahrwarner:17: error: lvalue required as left operand of assignment

pinMode(21, 20, 19, 18, 17, 15=OUTPUT);

Vorw_rtsfahrwarner:18: error: lvalue required as left operand of assignment

digitalWrite(15, 17, 18, 19, 20, 21=HIGH);

C:\Users\Stephan\Desktop\Vorw_rtsfahrwarner\Vorw_rtsfahrwarner.ino: In function 'void loop()':

Vorw_rtsfahrwarner:25: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:57: error: lvalue required as left operand of assignment

digitalWrite(21=LOW);

Vorw_rtsfahrwarner:58: error: lvalue required as left operand of assignment

digitalWrite(20=HIGH);

Vorw_rtsfahrwarner:59: error: lvalue required as left operand of assignment

digitalWrite(19=LOW);

Vorw_rtsfahrwarner:60: error: lvalue required as left operand of assignment

digitalWrite(18=LOW);

Vorw_rtsfahrwarner:61: error: lvalue required as left operand of assignment

digitalWrite(17=LOW);

Vorw_rtsfahrwarner:62: error: lvalue required as left operand of assignment

digitalWrite(15=HIGH);

Vorw_rtsfahrwarner:66: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:67: error: lvalue required as left operand of assignment

digitalWrite(20=LOW);

Vorw_rtsfahrwarner:68: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:69: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:70: error: lvalue required as left operand of assignment

digitalWrite(17=HIGH);

Vorw_rtsfahrwarner:71: error: lvalue required as left operand of assignment

digitalWrite(15=LOW);

Vorw_rtsfahrwarner:75: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:76: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:77: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:78: error: lvalue required as left operand of assignment

digitalWrite(18=HIGH);

Vorw_rtsfahrwarner:79: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:80: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:84: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:85: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:86: error: lvalue required as left operand of assignment

digitalWrite(19=HIGH);

Vorw_rtsfahrwarner:87: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:88: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:89: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:93: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:94: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:95: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:96: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:97: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:98: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:102: error: lvalue required as left operand of assignment

digitalWrite(21=HIGH);

Vorw_rtsfahrwarner:103: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:104: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:105: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:106: error: lvalue required as left operand of assignment

Vorw_rtsfahrwarner:107: error: lvalue required as left operand of assignment

C:\Users\Stephan\Desktop\Vorw_rtsfahrwarner\Vorw_rtsfahrwarner.ino: At global scope:

Vorw_rtsfahrwarner:111: error: expected unqualified-id before '{' token

Vorw_rtsfahrwarner:117: error: expected declaration before '}' token

exit status 1 lvalue required as left operand of assignment

The code of my projekt:

#include <LiquidCrystal.h> int trigger=7; int echo=6; long dauer=0; LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

long entfernung=0;

void setup() { Serial.begin (9600);

pinMode(trigger, OUTPUT); pinMode(echo, INPUT); pinMode(10, OUTPUT); lcd.begin(16, 2); pinMode(21, 20, 19, 18, 17, 15=OUTPUT); digitalWrite(15, 17, 18, 19, 20, 21=HIGH); }

void loop() { { delay(2000); digitalWrite(15, 17, 18, 19, 20, 21=HIGH); } digitalWrite(trigger, LOW);

delay(5); digitalWrite(trigger, HIGH); delay(10); digitalWrite(trigger, LOW); dauer = pulseIn(echo, HIGH);

entfernung = (dauer/2) / 29.1;

if (entfernung >= 500 || entfernung <= 0) { Serial.println("Kein Messwert"); } else { Serial.print(entfernung-1); Serial.println(" cm"); lcd.setCursor(0, 0);

lcd.print("Abstand[+/- 1cm]:");

lcd.setCursor(0, 1);

lcd.print(entfernung-1); lcd.print(" cm"); } { if (entfernung=2) { digitalWrite(21=LOW); digitalWrite(20=HIGH); digitalWrite(19=LOW); digitalWrite(18=LOW); digitalWrite(17=LOW); digitalWrite(15=HIGH); } if (entfernung=5) { digitalWrite(21=LOW); digitalWrite(20=LOW); digitalWrite(19=LOW); digitalWrite(18=LOW); digitalWrite(17=HIGH); digitalWrite(15=LOW); } if (entfernung=8) { digitalWrite(21=LOW); digitalWrite(20=LOW); digitalWrite(19=LOW); digitalWrite(18=HIGH); digitalWrite(17=LOW); digitalWrite(15=LOW); } if (entfernung=10) { digitalWrite(21=LOW); digitalWrite(20=LOW); digitalWrite(19=HIGH); digitalWrite(18=LOW); digitalWrite(17=LOW); digitalWrite(15=LOW); } if (entfernung = 12) { digitalWrite(21=LOW); digitalWrite(20=HIGH); digitalWrite(19=LOW); digitalWrite(18=LOW); digitalWrite(17=LOW); digitalWrite(15=LOW); } if (entfernung>12) { digitalWrite(21=HIGH); digitalWrite(20=HIGH); digitalWrite(19=LOW); digitalWrite(18=LOW); digitalWrite(17=LOW); digitalWrite(15=LOW); } } } { delay(1000); lcd.setCursor(0, 1); lcd.print(" "); digitalWrite(anzeige=LOW); } }

Please help me AS SOON AS POSSIBLE!

Vorw_rtsfahrwarner.ino (2.04 KB)

Have a read of the reference pages for the functions that are causing you the errors and see if you can spot what you're doing wrong:

. . . and when you've read that, please read the posting guidelines at the top of this section of the forum.

PS you may also want to review some of the comparisons in your if() statements.

I don't know what language that is, but it is not C/C++.

Look at the examples and copy that syntax.

Muss die Hausaufgabe morgen abgegeben werden?

Is the assignment due tomorrow?