请大神解答下为什么我的程序不能循环
#include<stdio.h>
int main()
{
float c,f;
char a;
a='y';
while(a!='n')
{
printf("please enter numer:\n");
scanf("%f",&f);
c=(5.0/9)*(f-32);
printf("the result is:%f\n",c);
printf("whether keep on? y or n\n");
scanf("%c",&a);
}
}
