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ccomma-operator

comma vs && operator in loops and if-else

Consider the code:

if(x = a/b, a%b) 
 printf("do this");
else 
 printf("do that");

Now if I replace if statement by if(x = a/b && a % b). Then it works also. So I want to know that replacing comma by && operator and vice-versa works always or not in if-else and loops

Solution

  • They are quite different!

    In the first example, , is the comma operator, which is a binary operator that evaluates its first operand and discards the result, and then evaluates the second operand and returns this value (and type).

    So, 

    if(x = a/b, a%b)

    is equivalent to (thanks to @jaket)

    x = a/b;
if(a%b)

    a%b will always be evaluated.

    For the second one:

    if(x = a/b && a % b)

    is equivalent to

    x = (a/b) && (a%b);
if( x )

    a%b will only be evaluated if a/b (i.e. a/b is not zero) is true.