Help! C beginner needs help with dealing with inputs to a scanf() function!

Hi

I have written a very basic program that asks for people to input a number and it works out the factorial of that number and displays it to the screen. However, when people enter a letter instead of a number, the program goes on an unstoppable loop. How can I detect whether a user has entered a letter and deal with it before this happens?

Any help greatly apprecitated!

Thanks

Jamie

Code:

---

if((isalpha(input)) == TRUE){
    /*code to handle a letter*/
}else{
    /*code for proper input*/
}

---

But I think the problem still remains there...
If the user inputs .,/= etc. Then???

which library is isalpha() in? Because I can't find it!

Thanks

Jamie

check ctype.h i think

> (isalpha(input)) == TRUE
In addition, isalpha doesn't return TRUE - it returns non-zero if the character passes the test

So

Code:

---

if ( isalpha(input) ) {
    // its a letter
} else {
    // no it isn't
}

---

Hmm.. maybe this will be helpful.

Program with problems...

Code:

---

#include <stdio.h>
int main ()
{
 int i;
 printf ("Type in numbers, foo!\nType in 0 to quit!\n");
 while ()
 {
  scanf ("%d", &i);
  if (i == 0) break;
  printf ("You typed in %d\n", i);
 }
 return 0;
}

---

And the program without the same problems...

Code:

---

#include <stdio.h>
int main ()
{
 int i, j;
 printf ("Type in numbers, foo!\nType in 0 to quit!\n");
 while ()
 {
  j = scanf ("%d", &i);

  if (j != 1)
  {
  printf ("That ain't a number, get outta my program!\n");
  break;
  }

  if (i == 0) break;
  printf ("You typed in %d\n", i);
 }
 return 0;
}

---

Just trying to take advantage of the fact that scanf returns the number of arguments scanned in, or EOF if EOF is encountered. So basically, in that call of scanf, it is going to either return 1, which means it succesfully scanned something in, a 0 which means it couldn't read any arguments (because the first one wasn't an int), or EOF, which shouldn't matter unless you use a file as stdin.

As usuall, I'm not -sure- that the programs 'll work, but I like to inagine they do.

> int main ()
> {
> int i;
> printf ("Type in numbers, foo!\nType in 0 to quit!\n");
> while ()

You seem to have acquired some bad programming habbits there.
Both your 'main' and your 'while' should not be empty. This is just sloppy programming.

Quzah.

Thank you all very much!

I now have a working program.

Drinks on me.... =)

Hi, I'm curious about how your code looks now that is working. Would you post it?

Thanks