c++cif-statementlogical-operatorsequals-operator

Why does (0 && 1 == 0) not evaluate to true?

In my if statement, the first condition for && is 0 (false), so the expression 0 && (a++) is equal to 0, right? Then 0==0 it should be true. Why am I getting else here? Please explain!

int a=0;
if(0 && (a++)==0)
{
    printf("Inside if");
}
else
{
    printf("Else");
}
printf("%i",a);
Solution

  • The == operator has a higher priority than the && operator, so this line:

    if(0 && (a++)==0)

    is treated like this:

    if(  0 && ((a++)==0) )

    So the whole expression under the if is false, and a++ is not even evaluated due to short circuitry of the && operator.

    You can read about Operator Precedence and Associativity on cppreference.com.

    When in doubt, you should use parenthesis to express your intention clearly. In this case, it should be:

    if( (0 && (a++)) == 0  )

    Though, it does not make any sense, as it always evaluates to true and a++ is not incremented here, either.