C古典関数ポインタの使用

定義方法:int(*p)(int x,int y);

#include <stdio.h>
int sum(int x, int y){
    return  x + y;
}
int reduce(int x, int y){
    return x - y;
}
int multiply(int x, int y){
    return  x * y;
}
float divide(int x, int y){
    if(y ==0)
        return 0;
    else
        return  x *1.0f/ y;
}

int main(int argc, const char * argv[])
{

    // 1.      
    int (*p)(int x, int y);
    // 2.   
    p = sum;
    // 3.  
    int s = p(3,2);
    // 4.  
    printf("%d
",s);//=5;

    //--------------
    printf("     1,2,3,4
");
    int num;
    scanf("%d",&num);

    switch (num) {
        case 1:
            p = sum;
            break;
        case 2:
            p = reduce;
            break;
        case 3:
            p = multiply;
            break;
        case 4:
            p = divide;
            break;

    }
    int result = p(22,2);

    printf("%d
",result);

    return 0;
}