Input validation using C

Question

I'm writing a program to prompt the user to enter a number between 1 and 5. If the value is greater than 5 or less than 1 I want the program to wait until an appropriate answer is given. This is what I came up with and it's not working. I've tried a few different tips off the net and it still isn't working. Any tips would be great, thanks.

#include <stdio.h>

int main()
{
    int p1_move;

    do{                         
        printf("1  \n 2 \n 3 \n 4 \n 5\n");
        printf("Player 1, enter the number:\n");
        scanf("%d", &p1_move);
    }while(p1_move >=6 || <=0);         
}

while(p1_move >=6 || p1_move <=0);

Pankrates
– Pankrates

2013-10-08 01:49:15 +00:00
Commented Oct 8, 2013 at 1:49 — Pankrates
– Pankrates, Commented Oct 8, 2013 at 1:49

paddy · Accepted Answer · 2013-10-08 01:49:15Z

3

You need a variable for each test:

while(p1_move >=6 || p1_move <=0);

You also have potentially undefined behaviour here:

scanf("%d", &p1_move);

You do not test whether the input was successful. If the input failed first time around (eg EOF or non-integer input), p1_move will remain uninitialised.

answered Oct 8, 2013 at 1:49

paddy

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Comments

Yu Hao · Accepted Answer · 2013-10-08 01:49:13Z

1

Your code shouldn't compile.

Change

while(p1_move >=6 || <=0);

to

while(p1_move >=6 || p1_move <=0);

answered Oct 8, 2013 at 1:49

Yu Hao

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4 Comments

KThund Over a year ago

Thanks, this worked. Alternatively, would there be a way to make the while statement say anything that ISN'T 1/2/3/4/5? I thought it was !1!2!3!4!5

Yu Hao Over a year ago

@KThund Not really, !a results as 0 for all non-zero a, results as 1 for zero. You still need to test them separately like a != 1 && a !=2 && a != 3 etc.

KThund Over a year ago

Sorry, I don't understand. I was thinking of making it so if any character or number other then 1,2,3,4or5 is entered it will repeat the same prompt. Is it possible to do this?

Yu Hao Over a year ago

@KThund I'm not saying the logic is wrong. I'm saying the syntax should be like while (a != 1 && a !=2 && a != 3).

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