排序算法----调用库函数qsort进行快速排序

功 能： 快速排序

头文件：stdlib.h

用 法： void qsort(void *base,int nelem,int width,int (*fcmp)(const void *,const void *));

参数： 

1 待排序数组首元素的地址 

2 数组中待排序元素数量

3 各元素的占用空间大小

4 指向函数的指针，用于确定排序的顺序

注意：数组中可以存储数字，字符，或者结构体都行。

数字：

 #include <stdio.h>
 #include <stdlib.h>  

 int compInc(const void *a, const void *b)
 {
     return *(int *)a - *(int *)b;
 }

 int compDec(const void *a, const void *b)
 {
     return *(int *)b - *(int *)a;
 }

 int main()
 {
     int a[] = { ,,,, };
     int len = ;
     int i;

     printf("递增排序结果:\n");
     qsort(a, len, sizeof(a[]), compDec);
     for (i = ; i < len; i++)
     {
         printf("%d ", a[i]);
     }
     printf("\n");

     return ;
 }

字符串长度排序：

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #define M 12
 #define N 20  

 int compareInc(const void *a, const void *b)
 {
     return strlen((char *)a) - strlen((char*)b);//字符串长度比较
 }

 int compareDec(const void *a, const void *b)
 {
     return strlen((char *)b) - strlen((char*)a);
 }

 int main(void)
 {
     int i;
     char s[M][N] =
     {
         "January",
         "February",
         "March",
         "April",
         "May",
         "June",
         "July",
         "August",
         "September",
         "October",
         "November",
         "December"
     };

     qsort(s, M, sizeof(char) * N, compareInc);
     for (i = ; i < M; i++)
         printf("%s\n", s[i]);

     printf("\n");

     qsort(s, M, sizeof(char) * N, compareDec);
     for (i = ; i < M; i++)
         printf("%s\n", s[i]);

     return ;
 }

字符串大小排序：

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #define M 12
 #define N 20  

 int compare1(const void *a, const void *b)
 {
     return *(char *)a - *(char*)b;//字符串大小比较
 }

 int compare2(const void *a, const void *b)
 {
     return *(char *)b - *(char*)a;
 }

 int main(void)
 {
     int i;
     char s[M][N] =
     {
         "January",
         "February",
         "March",
         "April",
         "May",
         "June",
         "July",
         "August",
         "September",
         "October",
         "November",
         "December"
     };

     qsort(s, M, sizeof(char) * N, compare1);
     for (i = ; i < M; i++)
         printf("%s\n", s[i]);

     printf("\n");

     qsort(s, M, sizeof(char) * N, compare2);
     for (i = ; i < M; i++)
         printf("%s\n", s[i]);

     return ;
 }

结构体：

 #include <stdio.h>
 #include <stdlib.h>
 #define N 6  

 typedef struct
 {
     char name[];
     int  score;

 }Student;

 int compare1(const void *a, const void *b)
 {
     return ((Student*)a)->score - ((Student*)b)->score;//以结构体的成绩排序
 }

 int compare2(const void *a, const void *b)
 {
     return *(((Student*)a)->name) - *(((Student*)b)->name);//以结构体的学生姓名排序
 }

 void print(Student s)
 {
     printf("%-15s : %d\n", s.name, s.score);
 }

 int main()
 {
     Student s[N] =
     {
         "Zhang San", ,
         "Li Si",     ,
         "You",       ,
         "I",        ,
         "He",        ,
         "She",
     };

     int i;
     qsort(s, N, sizeof(Student), compare1);
     for (i = ; i < N; i++)
     {
         print(s[i]);
     }

     printf("\n");

     qsort(s, N, sizeof(Student), compare2);
     for (i = ; i < N; i++)
     {
         print(s[i]);
     }

     return ;
 }