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Lvalue Required As Left Operand Of Assignment C++ Code

 

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:

  1. The value of c should be stored in 3a + 2b which is not possible and does not make sense either.
  2. 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

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.

Solution

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.

Solution

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.

Related

#include<stdio.h>

 

intmain()

{

      intc,x,y;

      2*x+3*y=c;

      printf("\nValue of Expression:\t%d",c);

      return0;

}

#include<stdio.h>

 

intmain()

{

      intc,x,y;

      c=2*x+3*y;

      printf("\nValue of Expression:\t%d",c);

      return0;

}

1

if(strcmp("CodingAlpha","CodingAlpha")=0)

1

if(strcmp("CodingAlpha","CodingAlpha")==0)

Category: C Programming

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.

Example:

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

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

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

Solve error: lvalue required as left operand of assignment

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

Example 1:

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.

Example 2:

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.

Example 3:

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.

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


#include<stdio.h>

 

intmain(){

    inta=5,b=5;

 

    if(a%b=0)

        printf("its crazy");

 

    return0;

}

#include<stdio.h>

 

intmain(){

    inta=5,b=5;

 

    if(a%b==0)

        printf("its crazy");

 

    return0;

}

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#include<stdio.h>

 

intfindFact(intn){

    intans=1,i;

    

    for(i=1;i<=n;i++){

        ans*i=ans;

    }

 

    returnans;

}

 

intmain(){

    intn=5;

    intfact=findFact(n);

    printf("%d",fact);

 

    return0;

}

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#include<stdio.h>

 

intfindFact(intn){

    intans=1,i;

    

    for(i=1;i<=n;i++){

        ans*=i;

    }

 

    returnans;

}

 

intmain(){

    intn=5;

    intfact=findFact(n);

    printf("%d",fact);

 

    return0;

}

// misunderstanding ternary operator

#include<stdio.h>

 

intmain(){

    inta=5,b;

 

    a>=5?b=10:b=19;

 

    return0;

}

#include<stdio.h>

 

intmain(){

    inta=5,b;

 

    b=a>=5?10:19;

 

    return0;

}

Category: C Tutorials

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