Thread: isdigit() Function!

  1. #1
    Registered User
    Join Date
    May 2008

    isdigit() Function!

    Hi guys, here is the code:

    #include <stdio.h>
    #include <stdlib.h>
    #include <ctype.h>
    int main()
    	int iYearBorn = 0;
    	printf("\nEnter year born, either 2000, 2001, 2002: ");
    	scanf("%d", &iYearBorn);
    		if (isdigit(iYearBorn) == 0)
    				printf("\nInvalid Entry. Not a number! Program Terminating.\n");
    				return 0;
    			case 2000:
    			printf("\n2000 is the year of luck!\n");
    			case 2001:
    			printf("\nPeace be with you 2001\n");
    			case 2002:
    			printf("\n2002 is uber leet pwnage dudez\n");
    			printf("\nNo data on that year!\n");
    	return 0;
    What I want to do is check the user's input to make sure it's a number, if it's not a number I want it to display that message (Invalid Entry. Not a number! Program Terminating) and kill the program.

    If it is a number I want it to continue on down to the switch statement etc, but the problem is, whenever I run it, no matter what the user input is, it ALWAYS says "Invalid Entry. Not a number! Program Terminating" and kills the program, even if I enter a number... so I'm assuming i'm using the isdigit function wrong somehow, if anyone could help me out that'd be great. Thanks!

  2. #2
    Hurry Slowly vart's Avatar
    Join Date
    Oct 2006
    Rishon LeZion, Israel
    isdigit checks the character, not a number

    so '1' is digit, and 'a' is not...

    to make verification as you want - you need to read the user input as string for example using fgets

    then - try to convert it using strtol for example and see where the conversion stops, if all characters of the string except \n are successfully parsed - it was a valid number, if something left in the buffer - it is not
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

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