Need help please. Need to validate only numerical input.

hello fellow coders. i have a slight problem with getting to validate the input.
the thing is, i want the user to be able to input only numbers in here:

Code:

---

printf("ENTER GUESS 1: ");
scanf("%d",&guess[0]);

printf("ENTER GUESS 2: ");
scanf("%d",&guess[1]);

printf("ENTER GUESS 3: ");
scanf("%d",&guess[2]);

printf("ENTER GUESS 4: ");
scanf("%d",&guess[3]);

---

could someone with more experience please help.
much appreciated.

Hey look a FAQ

thnx for that. ive read through it, but the thing is i dont really understand how i could do it. the thing is i actually want the user to be able to input only numbers, and if they input a letter an error message to display and then for them ot be able to try again.
perhaps someone has done this before? and they could help?
thnx.

So read in the input as string, then check if the string consists entirely of numbers. If so, convert it to a number type, else get the user to try again.

>the thing is i actually want the user to be able to input only numbers
You can't force the user to input only what you expect in standard C. You can certainly use a non-standard non-blocking read to enforce that kind of behavior:

Code:

---

#include <ctype.h>
#include <stdio.h>
#include <conio.h>

#define ESC 0x1B

int main ( void )
{
  int ch;

  printf ( "Enter a number: " );
  fflush ( stdout );

  while ( ( ch = getch() ) != ESC ) {
    if ( isdigit ( ch ) )
      putchar ( ch );
  }

  printf ( "\n" );

  return 0;
}

---

But that's not portable, and I'd question why reading a string completely and then validating it using standard functions isn't sufficient.

yes, ummm. i think i know what i have to do know.
read the string completely, check if its only numbers, if not display error and try again.

could someone perhaps point me in the right direction how i could go about doing this.
thnx.

You can start by looking here: http://faq.cprogramming.com/cgi-bin/...&id=1043284392

Todd

thnx guys.
i used this:

Code:

---


static void die ( char *msg )
{
  fprintf ( stderr, "%s\n", msg );
  exit ( EXIT_FAILURE );
}

int main ( void )
{
int guess[4];

printf("ENTER GUESS 1: ");
                if (scanf("%d",&guess[0]) != 1)
                        die ("INVALID");
}

---

the above code works fine, but it could be improved.
at the moment it displays INVALID and then quits.

can someone please tell me how i can prevent it from quitting, but rather ask the user to input GUESS 1 again??
thnx.

Did you try a loop?

Code:

---

int valid = 0;

while ( !valid ) {
  printf("ENTER GUESS 1: ");
  fflush ( stdout );

  if (scanf("%d",&guess[0]) == 1)
    valid = 1;
  else
    printf ( "INVALID\n" );
}

---

Code:

---

static void die ( char *msg )
{
        fprintf ( stderr, "%s\n", msg );
        exit ( EXIT_FAILURE );
}

int main ( void )
{
        int guess[4];
        printf("ENTER GUESS 1: ");
        if (scanf("%d",&guess[0]) != 1)
                die ("INVALID");
}

---

You should also learn to indent properly and not mix spaces and tabs--you can use one.
Oh and, you know, think a little of how the program works. If I entered something in an app and it wasn't valid input and the program quit saying "invalid data", I'd be rather annoyed. Wouldn't you?
Yes, the program should say invalid data, but it shouldn't quit.
(And what's with a static function? I don't think I've encountered a static global function before.)

>And what's with a static function?
It's a function with internal linkage. Functions have external linkage by default, but sometimes you don't want them to be visible to everyone.

Quote:

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Originally Posted by Prelude

Did you try a loop?

---

i used that code but then it just kept on looping and saying invalid loop after loop unable to stop.

Quote:

---

Originally Posted by Prelude

>And what's with a static function?
It's a function with internal linkage. Functions have external linkage by default, but sometimes you don't want them to be visible to everyone.

---

Oh, right. In C everything is external by default. I completely forgot.
Thanks for clearing that up, though.

Quote:

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Originally Posted by oli3

i used that code but then it just kept on looping and saying invalid loop after loop unable to stop.

---

Did you try reading a line from the input with fgets?

>i used that code but then it just kept on looping and saying invalid loop after loop unable to stop.
My bad, I was in too much of a hurry. When scanf errors, it leaves the unconverted characters in the stream. So you have to remove them or scanf will continue to error on the same bad input:

Code:

---

int valid = 0;

while ( !valid ) {
  printf("ENTER GUESS 1: ");
  fflush ( stdout );

  if (scanf("%d",&guess[0]) == 1)
    valid = 1;
  else {
    printf ( "INVALID\n" );

    while ( getchar() != '\n' )
      ;
  }
}

---

Quote:

---

Originally Posted by Prelude

>i used that code but then it just kept on looping and saying invalid loop after loop unable to stop.
My bad, I was in too much of a hurry. When scanf errors, it leaves the unconverted characters in the stream. So you have to remove them or scanf will continue to error on the same bad input:

Code:

---

int valid = 0;

while ( !valid ) {
  printf("ENTER GUESS 1: ");
  fflush ( stdout );

  if (scanf("%d",&guess[0]) == 1)
    valid = 1;
  else {
    printf ( "INVALID\n" );

    while ( getchar() != '\n' )
      ;
  }
}

---

---

thats working 100%..
u just dont know how thankful i am!!! now im just gonna implement it into the other 3 guesses.
cheers !

You could make that into a function too, if you want a nice and healthy exercise!