请解释一下这个C代码片段mult（x，y）x * y？

Question

#include <stdio.h>
#define mult(x,y)x*y  /* what does this mean ?? */

int main() 
{
  int a,b,answer;
  b=5;
  a=5;

  answer=mult(a+b,a+b);
  printf("%d",answer);

  return 0;
}

I'm using compiler gcc-4.9.2

Answer 1

If I understand correctly you want to know what #define mult(x,y) x*y does.

This a definition of a macro, during the compilation the compiler will replace, everywhere in the code, mult(x, y) by x*y .

In your code: answer=mult(a+b,a+b);

Will be replaced by: answer=a+b*a+b;

Whence the answer will be 35 .

A correct way to use macros and to ensure they work properly is to include parentheses where they might be needed.

Therefore your define would be: #define mult(x, y) ((x)*(y)) to ensure the result is what you would expect 100