Thread: Checking input in a while loop...

This is what I have for this particular function so far...

Code:

unsigned long getNum(char prompt[80])
{
   unsigned long darts;
   printf("%s", prompt);
   while((scanf("%lu", &darts)) != 1)
   {  
      printf("\n\nThis is not an acceptable entry. please try again.\n");
      printf("%s", prompt);
   }
   return darts;
}

it works perfectly fine if I enter a number. but if i enter a character or letter or something, i was expecting it to reprompt, but instead it goes into an infinite loop of prompting and error messages. Can someone explain why? How can I fix it?