全班 N 个学生，每个学生有学号、姓名、年龄，需要按照年龄进行排序.

#include <stdio.h>
#include <math.h>
#include <string.h>
#define N 5

typedef struct student {
  char num[10];
  char name[20];
  int age;
}stud;

void swap_student(struct student *a, struct student *b) {
	stud tmp;
	tmp = *a;
	*a = *b;
	*b = tmp;
}

void sort_soap(struct student list[], int len)
{
    int i, j;
    for (j = 0; j < len-1; j++) {
        for (i = 0; i < len-j-1; i++) {
            if (list[i].age > list[i+1].age) {
				//交换相邻的两个数
				swap_student(&list[i], &list[i + 1]);
			}
		}
    }
}

void main(void)
{
	//初始化数据
	int i;
	stud list[N]={
		{"2017001","张三",22},
		{"2017002","李四",21},
		{"2017003","王五",18},
		{"2017004","赵六",19},
		{"2017005","丁一",20},
	};
	
	//排序
    sort_soap(list, N);

	//打印
    for(i = 0; i < N; ++i) {
        printf("%s %s %d\n",list[i].num, 
			list[i].name, list[i].age);
    }
}