Thread: problem with scanf function

Hi everyone. The problem I have looks very stupidly at the first sight and I am sorry for posting it. But even if I searched reference manuals and already posted questions in forums around the net, I wasn’t able to solve that.

Could you anyone please tell me, why this isn’t working?

Code:

  int nr,err;
  do {
   printf("\nenter a number (0-10):");
   err=scanf("%d",&nr);   
   if(err==1&&(nr<0||nr>10)) printf("the number must be between 0 and 10\n");   
  }while(err!=1||(err==1&&(nr<0||nr>10)));

It works fine when you enter a good value, it works also when you enter wrong value, but digit. If you enter a character, it will start an unending repeating. Why doesn’t it ask to reenter the value?

The only tips I’ve found was about flushall() function; I am not sure if it would be usable in my case too, but I can’t use that either – I have to do this in C not in C++.

Thanks for any tips or links somewhere where relevant information could be found.

It doesn't ask because the part of the if statement isn't true -- if you type in "bob", the scanf is unable to process %d, so (a) "bob" is left in the input stream (this is why it just keeps repeating) and (b) err is set to 0. Since err is set to 0, your if doesn't trigger, but you do-while loop will loop. Since there's still stuff left in the input stream, scanf doesn't wait for more input but keeps trying to read what's there.

You can read the FAQ about getting numbers for some ideas; there's also an FAQ about how to get rid of bad input typed in as well.