1、sum函数定义如下：int sum(int x, int y) /*对函数sum()进行定义*/ { return x + y;} 2、C代码如下：include <stdio.h> int f(int n) { // 返回n!int i, s = 1;for (i = 1; i <= n; i++)s = s * i;return s;} int main() { int sum = f(4) + f(6)...