Thread: isdigit() to validate if input is number..

Hi..
i have a doubt..
i have seen that isdigit() function is used with "character" data type..
but can we use to validate an "integer"...??
i mean is it ok..to write like this..

Code:

int num;
scanf("%d",&num);
if(isdigit(num))
{
  printf("you entered a number..");
}
else
{
  printf("enter only an integer number..");
}

My task is to check the input given by user..whether it is an INTEGER or not..
Kindly help me..
thank you.

Check the return value of scanf instead.

I did not get you.on the above statement.

can you please show me a small program on how to check user input.
i want the user to tell
1.if he enters a character..i want to tell him to enter only integers not characters.
2.if he enters a valid integer..but a negative one..then i have to prompt the user..not to enter negative numbers..
Thank you.

O_o

You pretty much have to read the input as a string (as laserlight says) and then attempt the conversion checking the result and the consumed length of input.

Soma

@@phantomotap..

A small program PLEASE..!!
it would help me a lot..!!

Thank you.

but can we use to validate an "integer"...??

It would take literally one minute to write up a little program to test this question. Have you tried that? I'd guess not, since you're asking.

My task is to check the input given by user..whether it is an INTEGER or not..

Read up on the return type of "scanf()" - this will give you insight on how to validate the user's input.

EDIT: Oops, let the page sit too long! Didn't know everyone else was in on this one.

this is the program that i wrote ... for adding the digits in a number..
I USED THE CODE GIVEN BY SALEM TO WRITE THE PROGRAM.
Somehow it's not working..

Code:

#include <stdio.h>
#include <stdlib.h>

int sumofidigits(int);


int main()
{
    int num,sum = 0;
    printf("Enter a non-negative number\n");
    if(scanf("%d",&num) == 1);
    {
      sum = sumofidigits(num);
      printf("Sum of the digits is %d",sum);
    }
   
   return 0;
}
int sumofidigits(int x)
{
    int rem,sum = 0;
    while(x>0)
    {
        rem = x % 10;
        x = x / 10;
        sum = rem + sum;
    }
    return(sum);
}

thank you.

@@laserlight,@@Matticus ,@@Salem,@@phantomotap
Thanks for your help.
I have now sorted it out.
But today i learnt something about "scanf" which i did not know earlier.
Once again thanks for taking time and explaining everything.

Thank You.