在C语言中，sign函数通常用来返回一个数的符号，即判断一个数是正数、负数还是零。其原型定义为：

int sign(int x);

参数x为要判断符号的数，函数返回值为：

示例代码如下：

#include <stdio.h>int sign(int x){if(x > 0){return 1;}else if(x == 0){return 0;}else{return -1;}}int main(){int num = 10;printf("The sign of %d is: %d\n", num, sign(num));num = -5;printf("The sign of %d is: %d\n", num, sign(num));num = 0;printf("The sign of %d is: %d\n", num, sign(num));return 0;}

输出结果为：

The sign of 10 is: 1The sign of -5 is: -1The sign of 0 is: 0