Question

The preprocessor directive which checks whether a constant expression results in a zero or non-zero value __________

(a) #if

(b) #ifdef

(c) #undef

(d) #ifndef

Answer 1

Correct choice is (a) #if

The best explanation: #if checks whether a constant expression results in zero or not. If the expression is a non-zero value, then the statements between #if and #endif will be executed.  If the constant expression results in a zero value, the statements between #if and #endif will not be executed.