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("\nSorted list:");
     showarray(vals, NUM);

     return ;
 }

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

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

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

     if (index %  != ) putchar('\n');
 }

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

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

qsorter.c