C语言基础 指针·通用排序

#include<stdio.h>
#define N 40          //输入个数的上限
int readscore(int score[])  //读取数据函数
{
    int i=-1 ;
    do
    {
        i++;
        printf("Input score: ");
        scanf("%d",&score[i]);
    }while(score[i]>=0);                  //这个分号老是忘记
    return i;
}
void select(int a[],int n,int (*compare)(int a,int b))  //排序函数
{
    int i, j , k ;
    for(i=0;i<n-1;i++)
    {
        k = i ;
        for(j=i+1;j<n;j++)
        {
            if((*compare)(a[j],a[k]))  k = j ;
        }
        if(k!=j) swap(&a[k],&a[i]);
    }
}
int ascending(int a ,int b)  / /升序
{
    return a<b ;
}
int descending(int a,int b)  //降序  
{
    return a>b;
}
swap(int *x,int *y)  //交换函数
{
    int temp= *x;
    *x = *y;
    *y = temp;
}
void output(int score[],int n)   //输出函数
{
    int i=0;
    for(;i<n;i++)
    {
        printf("%4d",score[i]);
    }
}

int main()
{
    int score[N] , n  , order ;
    n = readscore(score);
    printf("Total students are %4d\n",n);
    printf("Input 1 to ascend \n");
    printf("Input 2 to descend \n");
    scanf("%d",&order);
    if(order = 1)
    {
        select(score,n,ascending);
        printf("data items in ascending order \n");
    }
    else
    {
        select(score,n,descending);
        printf("data in descending order \n");

    }
    output(score,n);
    return 0;

}