《C++程序设计POJ》《WEEK1 从C走进C++》函数指针

/*函数指针*/

#include<stdio.h>
void PrintMin(int a, int b)
{
    if (a < b)
        printf("%d\n", a);
    else
        printf("%d\n", b);
}

int main()
{
    void(*pf)(int, int);
    int x = 6, y = 5;
    //PrintMin(x, y);
    pf = PrintMin;
    pf(x, y);
    //while (1);
    system("PAUSE");
    return 0;
} 

//void qsort(void *base, int nelem, unsigned int width,
//    int(*pfCompare)(const void *, const void *)); //是 void * 类型


//int 比较函数名(const void * elem1, const void * elem2);
//比较函数编写规则：
//1) 如果 * elem1应该排在 * elem2前面，则函数返回值是负整数
//2) 如果 * elem1和* elem2哪个排在前面都行，那么函数返回0
//3) 如果 * elem1应该排在 * elem2后面，则函数返回值是正整数


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

int MyCompare(const void* elem1, const void* elem2)
{
    unsigned int *p1, *p2;
    p1 = (unsigned int*)elem1; // *elem1 非法，因为不知道数据类型
    p2 = (unsigned int*)elem2;
    //return  (*p1 % 10) - (*p2 % 10) ;
    return  (*p2 % 10) - (*p1 % 10);
    //return 0;
}
#define NUM 5
int main()
{

    unsigned int an[NUM] = { 8,123,11,10,4 };
    qsort(an, NUM, sizeof(unsigned int), MyCompare);
    for (int i = 0; i < NUM; i++)
        printf("%d ", an[i]);
    while (1);
    return 0;


}