当按下~（代字号）键时，break关键字与if命令一起

#include <stdio.h>
int main()
{
   char ch;
   puts("Start tyPing");
   puts("Press ~ then Enter to stop");
   for(;;)
   {
      ch=getchar();
      if(ch=='~')
      {
         break;
      }
   }
   printf("Thanks!\n");
   return(0);
}