User Entering Numbers

How can I verify that something enetered by a user is a number? I have a program to accept numbers from the user but I need to check each one as they enter them and make sure they are not enetering letters instead.

Check if scanf() succeed.

Code:

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

int main(void)
{
    int num;
   
    printf("Num: ");
    if((scanf("%d",&num)) == 1) {
        //all ok.. right input
        printf("You entered a number really, %d\n",num);
    }
   
    else {
        //invalid input.. error handling here
        printf("You entered, invalid data\n");
        printf("Shame on you :)\n");
    }
   
    system("PAUSE");
    return 0;
}

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or use isdigit() function to check if an input is numbers..