Thread: User Entering Numbers

  1. #1
    Registered User
    Join Date
    Jan 2003

    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.

  2. #2
    Registered User Vber's Avatar
    Join Date
    Nov 2002


    Check if scanf() succeed.
    #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");
        return 0;
    or use isdigit() function to check if an input is numbers..

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