第 16 章 C 预处理器和 C 库（qsort() 函数）

/*----------------------------------------
    qsorter.c -- 用 qsort() 排序一组数字
----------------------------------------*/

#include <stdio.h>
#include <stdlib.h>        //提供函数 rand() 原型

#define NUM 40

void fillarray(double ar[], int n);
void showarray(const double ar[], int n);
int mycomp(const void *p1, const void *p2);

int main()
{
    double vals[NUM];

    fillarray(vals, NUM);
    puts("Random list:");
    showarray(vals, NUM);

    qsort(vals, NUM, sizeof(double), mycomp);
    puts("
Sorted list:");
    showarray(vals, NUM);

    return 0;
}

void fillarray(double ar[], int n)
{
    for (int index = 0; index != n; ++index)
        ar[index] = (double)(rand()) / ((double)(rand()) + 0.1);
}

void showarray(const double ar[], int n)
{
    int index = 0;

    for (; index != n; ++index)
    {
        printf("%9.4f ", ar[index]);
        if (index % 6 == 5) putchar('
');
    }

    if (index % 6 != 0) putchar('
');
}

int mycomp(const void *p1, const void *p2)
{
    const double *a1 = (double*)p1;
    const double *a2 = (double*)p2;

    if (*a1 > *a2)
        return 1;
    else if (*a1 == *a2)
        return 0;
    else
        return -1;
}