用qsort()函數進行排序。__diff

/**********************************************************
*                                                                               *
*            用qsort()函數進行排序。                            *
*                                                                               *
**********************************************************/

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

#define N 11

 enum when{before,after};

 typedef enum  when when;

int cmp(const void *vp,const void *vq);
void fill_array(double *a,int n);
void prn_array(when val,double *a,int n);

int main(void)
{
    double a[N];
    fill_array(a,N);
    prn_array(before,a,N);
    qsort(a,N,sizeof(double),cmp);       ///在qsort函數體中指向數組a的元素的指標作為參數傳遞給cmp函數
    prn_array(after,a,N);
    return 0;
}

 

int cmp(const void *vp,const void *vq)
{
    const double *p=vp;
    const double *q=vq;
    double diff=*p - *q;

    return ((diff>=0.0)?((diff>0.0)?-1:0):+1);
}

void fill_array(double *a,int n)
{
    int i;
    srand(time(NULL));
    for(i=0;i<n;++i)
        a[i]=(rand()%1001)/10.0;  ///rand()%1001)產生一個位於0到1000之間的值，由於除以10.0，所以賦值給a[i]的值位於0-100之間
}
void prn_array(when val,double *a,int n)
{
    int i;
    printf("%s\n%s%s\n",
           "---",
           ((val==before)?"Before":"After"),"sorting:");
           for(i=0;i<n;i++)
           {
               if(i%6==0)
                putchar('\n');
               printf("%10.1f",a[i]);
           }
           putchar('\n');
}