求助 这个小C为什么不能while循环呢？

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
unsigned random(int n)
{ int k=5;
k=((k*159+23)%n)+1;
return k; }
main(){int num,
guess,
count;
int n=100;
char yes='Y';
printf("\nNow let us play the game, guess the number.\n");
while(toupper(yes)=='Y')
{ count=0; num=random(n);
do{
do {printf("\ninput yur number:");
scanf("%d",&guess); }while(!(guess>=1&&guess<=100));
if(guess<num)printf("your number is low! try again\n");
if(guess>num)printf("your number is high! try again\n");
count++;
if(count==15)
{printf("\nthe game is over,you can try again.");system("pause");exit(0); }}while(!(guess==num));
if(count<=7)printf("\nyou got it in %d time.",count);
else {printf("\nyou got it in %d time,you can do better the next time!");
printf("\n"); }
printf("\nNext?(Y/N):");
scanf("%c",&yes); }
system("pause");
return 0;}