#include <stdio.h>
int main()
{ 
   char ch,t;
   printf("Type a letter 'A' to 'M': ");
   scanf("%c",&ch);
   for(t ='A';t<='Z';t++)
   {
      putchar(t);
      if(t==ch)
         break;   
   }
   putchar('\n');
   return(0);
}

Type a letter 'A' to 'M': ABCDEFGHIJKLMNOPQRSTUVWXYZ