Question

#include <stdio.h> #define F(X,Y) X*Y main() { int a=3, b=4; printf("%d\n", F(a+b, a-b)); }

为什么答案是11

Answer 1

#include <stdio.h>

#define F(X,Y) X*Y

#define G(X,Y) (X)*(Y)

int main() {

int a = 3, b = 4;

printf("%d\n", F(a + b, a - b));// 宏展开式为：3 + 4*3 - 4，输出为: 11

printf("%d\n", G(a + b, a - b));// 宏展开式为：(3 + 4)*(3 - 4),输出为: -7

return 0;

}

Answer 2

F(a+b, a-b) = a+b*a-b = 3 + 4*3 - 4 = 11
所以，一般情况下，F宏是这么写的：
#define F(X,Y) ((X)*(Y))