Question

I’m trying to make a macro with the following formula: (a^2/(a+b))*b, and I want to make sure that the there will be no dividing by zero.

#define SUM_A( x, y ) if( x == 0 || y == 0) { 0 } else { ( ( ( x * x ) / ( ( x ) + ( y ) ) ) * ( y ) )}

and then I call the macro inside main:

float a = 40, b = 10, result; 
result = SUM_A(a, b); 
printf("%f", result);

I’ve tried using brackets around the if function but I keep getting syntax errors before the if statement. I’ve also tried using return, but I read somewhere that you’re not supposed to use that in define.

Answer 1

You can not use if statement, because #define is interpret by the preprocessor, and the output would be

 result=if( x == 0 || y == 0) { 0 } else { ( ( ( x * x ) / ( ( x ) + ( y ) ) ) * ( y ) )}

which is wrong syntax.

But an alternative is to use ternary operator. Change your define to

#define SUM_A( x, y )  ((x) == 0 || (y) == 0 ? 0 : ( ( ( (x) * (x) ) / ( ( x ) + ( y ) ) ) * ( y ) ))

Remember to always put your define between parentheses, to avoid syntax error when replacing.