問題描述：

以下使一個簡單的例子，用來說明指向函數(shù)的指針變量。定義兩個函數(shù)max和min，分別用來求最大值和最小值。在主函數(shù)中根據(jù)用戶輸入的數(shù)字是1或者是2，使指針變量指向max函數(shù)或者min函數(shù)。

codes:
#include <stdio.h>
int main()
{
    int max(int,int);//求最大值函數(shù)聲明 
    int min(int,int);//求最小值函數(shù)聲明 
    int (*p)(int,int);//定義指向函數(shù)的指針變量 
    
    int a,b,c,n;
    printf("please input two numbers:");//輸入兩個數(shù) 
    scanf("%d%d",&a,&b);
    printf("please choose 1 or 2:");//輸入1 or 2 
    scanf("%d",&n);
    if(n == 1){ //如果輸入1則使 p 指向max函數(shù) 
        p = max;
    }
    else if(n == 2){    //如果輸入2，使p指向min函數(shù) 
        p = min;
    }
    
    c = (*p)(a,b);
    printf("a = %d, b = %d\n",a,b);
    
    if(n == 1){
        printf("max = %d\n",c);
    }
    else{
        printf("min = %d\n",c);
    }
    return 0;
}

int max(int x, int y)   //求最大值函數(shù) 
{
    return x > y ? x : y;
} 

int min(int x, int y)   //求最小值函數(shù) 
{
    return x < y ? x : y;
}

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