c++ expression must be a modifiable lvalue [SOLVED]

Normally these type of c++ error occurs in conditional statments. For any conditional expression if we are using assignment operator(=) in-stand of comparison (==) then mostly c++ expression must be a modifiable lvalue error occurs.

1) c++ expression must be a modifiable lvalue (Scenario-1)

#include <iostream>
using namespace std;

int main()
{
    int A = 0; 
    int B = 1;
    int C = 1;

    // It is same as if ( (A + B) = C )
    if ( A + B = C ) // ERROR
    {
         std::cout << " Comparison match" << std::endl;
    }
        return 0;
}

Output:

Here we are assigning C variable to expression (A+B) so compiler is giving error of lvalue required as left operand of assignment. if we want to resolve this error then we have to use comparison (==) operator. Also always make sure to add brackets “(” and “)” for easy understanding and also to avoid any operator precedence errors.

SOLUTION :

    if ( (A + B) == C ) // SOLUTION using (==)
    {
         std::cout << " Comparison match" << std::endl;
    }

By modifying this code we can easily resolve lvalue required as left operand of assignment error from condition.

2) c++ expression must be a modifiable lvalue (Scenario-2)

#include <iostream>
using namespace std;

int main()
{
    int A = 0; 
    int B = 1;
    int C = 1;
    
    // Same as if ( (A == 0 && B) = C )
    if ( A == 0 && B = C ) // ERROR
    {
         std::cout << " Comparision match" << std::endl;
    }
        return 0;
}

Output:

SOLUTION :

    if ( (A == 0) && (B == C) ) // SOLUTION using (==)
    {
         std::cout << " Comparision match" << std::endl;
    }

Here assignment(=) operator has lower precedence then &&. So if we change assignment operator to comparison (==) operator then it has higher precedence so (A==0) && (B==C) condition will work proper and expression must be a modifiable lvalue error will be resolved.

CONCLUSION:

Whenever your c++ compiler get error for expression must be a modifiable lvalue, you always need to check below points

1. Check Assignment (=) operator is used in stand of comparison operator (==)
2. Check Operator precedence for expression is correctly applied
3. Try to use bracket for each expression and comparisons for avoiding mistakes

SEE MORE:

https://mrcodehunter.com/what-is-cpp-used-for-real-world-applications/