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[5] = { 11,2,13,4,7 };
    int len = 5;
    int i;

    printf("递增排序结果:\n");
    qsort(a, len, sizeof(a[0]), compDec);
    for (i = 0; i < len; i++)
    {
        printf("%d ", a[i]);
    }
    printf("\n");

    return 0;
}

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 = 0; i < M; i++)
        printf("%s\n", s[i]);

    printf("\n");

    qsort(s, M, sizeof(char) * N, compareDec);
    for (i = 0; i < M; i++)
        printf("%s\n", s[i]);

    return 0;
}

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 = 0; i < M; i++)
        printf("%s\n", s[i]);

    printf("\n");

    qsort(s, M, sizeof(char) * N, compare2);
    for (i = 0; i < M; i++)
        printf("%s\n", s[i]);

    return 0;
}

结构体：

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

typedef struct
{
    char name[15];
    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", 94,
        "Li Si",     80,
        "You",       94,
        "I",        100,
        "He",        72,
        "She",       60
    };

    int i;
    qsort(s, N, sizeof(Student), compare1);
    for (i = 0; i < N; i++)
    {
        print(s[i]);
    }

    printf("\n");

    qsort(s, N, sizeof(Student), compare2);
    for (i = 0; i < N; i++)
    {
        print(s[i]);
    }

    return 0;
}