#include "stdio.h"
main()
{
int x,y,h,f, k='y';
while(k=='y')
{
printf("enter h,f:");
scanf("%d %d",&h,&f);
x=2*h-f/2;y=f/2-h;
if(x>=0&&y>=0)
printf("h=%d,f=%d\n x=%d,y=%d\n",h,f,x,y);
else
printf("fault\n");
printf("end?y/n\n");
scanf("%c",&k);
}
}

首先要把 k 定义为字符型
由于你在输入判断字符k的值之前，你已经有输入整型h、f的值，且在输入时是以回车键作为结束符的，此时系统将会把该回车键自动赋值给字符 k，因此无法实现循环
改变后程序为：

#include "stdio.h"
main()
{
int h,f;
float x,y;
char k='y',m;
while(k=='y')
{
printf("enter h,f:");
scanf("%d%d",&h,&f);

x=2*h-f/2.0;y=f/2.0-h;
if(x>=0&&y>=0)
printf("h=%d,f=%d\n x=%.2f,y=%.2f\n",h,f,x,y);
else
printf("fault\n");
printf("end?y/n\n");
scanf("%c",&k);
scanf("%c",&k);
}
}

 

[quote]以下是引用kacfeng在2011-6-13 23:58:42的发言：

#include "stdio.h"
main()
{
int x,y,h,f, k='y';
while(k=='y')
{
printf("enter h,f:");
scanf("%d %d",&h,&f);
x=2*h-f/2;y=f/2-h;
if(x>=0&&y>=0)
printf("h=%d,f=%d\n x=%d,y=%d\n",h,f,x,y);
else
printf("fault\n");
printf("end?y/n\n");
fflush(stdin);                          //清除键盘流
scanf("%c",&k);
}
}

#include "stdio.h"
main()
{
int x,y,h,f;
 char k='y';
while(k=='y')
{
printf("enter h,f:");
scanf("%d %d",&h,&f);
x=2*h-f/2;y=f/2-h;
if(x>=0&&y>=0)
printf("h=%d,f=%d\n x=%d,y=%d\n",h,f,x,y);
else
printf("fault\n");
printf("end?y/n\n");
fflush(stdin);                        
scanf("%c",&k);
}
}

加一个getchar();