why does this code for finding if the user input is a number or a char does not work?

Asked May 01 '20 at 15:48

Active May 01 '20 at 15:50

Viewed 28 times

#include <stdio.h>

#include    <ctype.h>
int main()
{
    double number= 0.0;
    n1:
    printf(" Your number:");
    scanf("%lf",&number);
    getchar();
    if(!isdigit(number))
    {
       printf("not a number, please only numbers\n");
       goto n1;
    }
    else
    {
       printf("is a number");
    }
    return 0;

}

why doesnt this work? where did I make a mistake here ? Is the function isdigit() used correctly?

edited May 01 '20 at 15:50

Barmar

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asked May 01 '20 at 15:48

JustZero

2

Did you see the warnings? Did you read the docs of `isdigit`? – Eugene Sh. May 01 '20 at 15:50
`scanf()` won't put anything into `number` if it's not a valid number. – Barmar May 01 '20 at 15:51
1

Suggestion: mind your compiler diagnostics. Treat them as failures and correct the code before running the executable. – pmg May 01 '20 at 15:51
I don't think jumping back with `goto` instead of using a loop is going to win you many friends. – Christian Gibbons May 01 '20 at 15:53
@pmg You're assuming there were warnings. Godbolt gave me none , even with `-Wall`. – Spencer May 01 '20 at 15:53
Oops... my bad: a `double` value may be silently converted to `int` in some cases. – pmg May 01 '20 at 15:58
@pmg C certainly has a lot of ways to shoot yourself in the foot. – Spencer May 01 '20 at 15:59

why does this code for finding if the user input is a number or a char does not work?

0 Answers0