编写一个程序，用指向函数的指针数组执行菜单。例如，在菜单中选

#include <stdio.h>
#define F 4
float add(float x, float y);
float subtract(float x, float y);
float multiply(float x, float y);
float divide(float x, float y);
int main(void)
{
 char command[5];
 float x, y;
 float (*p[F])(float x, float y) = {add, subtract, multiply, divide};
 while(1)
 {
 printf("Select function:\n");
 printf("1 :  x + y\n");
 printf("2 :  x - y\n");
 printf("3 :  x * y\n");
 printf("4 :  x / y\n");
 printf("q :  quit\n");
 gets(command);
 if ( command[0] < '1' ||  command[0] > '4' ) break;
 printf("input x, y:");
 scanf("%f%f", &x, &y);
 getchar();
 printf("result is : %g\n", (*p[ command[0] - '1' ]) (x,y) );
 }
 return 0;
}
float add(float x, float y)
{
 return x + y ;
}
float subtract(float x, float y)
{
 return x - y ;
}
float multiply(float x, float y)
{
 return x * y ;
}
float divide(float x, float y)
{
 return x / y ;
}