Beginner C Question Help

**pmacdonald** · 07-10-2009

I'm currently reading C Programming for the Absolute Beginner and am stuck on one of the chapter questions. This is a really simple question but I am stuck.

Problem:
Build a number guessing game that uses input validation (isdigit() funciton) to verify that the user has entered a digit and not a non-digit (letter). Store a random number between 1 and 10 into a variable each time the program is run. Prompt the user to guess a number between 1 and 10 and alert the user if he was correct or not.

Code:

#include <stdio.h>
#include <ctype.h>

main()
{

    int iNumber = 0;
    int iAnswer = 0;
    srand(time());

    iAnswer = (rand() % 10) + 1;

    printf("Guessing Game\n");
    printf("\nGuess a number from 1 to 10: ");
    scanf("%d", &iNumber);

    if ( isdigit(iNumber) > 10 || < 1 )
        printf("Enter a number between 1 and 10");

        if (iNumber == iAnswer)
            printf("\nYou guessed right!\n");

        else
            printf("\nSorry, you guessed wrong\n");
            printf("The correct guess was %d\n", iAnswer);
}

I've already tried to run the program and debug it with no luck. I'm missing something from the text and obviously didn't apply that here.

Any help will be greatly appreciated,

-Peter

**BEN10** · 07-10-2009

Originally Posted by pmacdonald

I'm currently reading C Programming for the Absolute Beginner and am stuck on one of the chapter questions. This is a really simple question but I am stuck.

Problem:
Build a number guessing game that uses input validation (isdigit() funciton) to verify that the user has entered a digit and not a non-digit (letter). Store a random number between 1 and 10 into a variable each time the program is run. Prompt the user to guess a number between 1 and 10 and alert the user if he was correct or not.

Code:

#include <stdio.h>
#include <ctype.h>

main()
{

    int iNumber = 0;
    int iAnswer = 0;
    srand(time());

    iAnswer = (rand() % 10) + 1;

    printf("Guessing Game\n");
    printf("\nGuess a number from 1 to 10: ");
    scanf("%d", &iNumber);

    if ( isdigit(iNumber) > 10 || < 1 )
        printf("Enter a number between 1 and 10");

        if (iNumber == iAnswer)
            printf("\nYou guessed right!\n");

        else
            printf("\nSorry, you guessed wrong\n");
            printf("The correct guess was %d\n", iAnswer);
}

I've already tried to run the program and debug it with no luck. I'm missing something from the text and obviously didn't apply that here.

Any help will be greatly appreciated,

-Peter

To check correctly do this

Code:

isdigit(iNumber) > 10 || isdigit(iNumber)< 1

**Salem** · 07-10-2009

isdigit() is for chars, not ints.

> scanf("%d", &iNumber);
You can't use isdigit here, scanf has already done that for you with the %d conversion.

If you did this however

Code:

char ch;
scanf("%c",&ch);
if ( isdigit(ch) )

Then that would be better usage of the function.

**Sebastiani** · 07-10-2009

>> if ( isdigit(iNumber) > 10 || < 1 )

Do be sure to look up the documentation on a function before you use it.

Anyway, isdigit expects a *character* value and returns true or false (1 or 0). As it turns out you don't need the function at all here, just a straight comparison:

Code:

if ( iNumber > 10 || iNumber < 1 )

Next, this statement:

Code:

printf("The correct guess was %d\n", iAnswer);

If you want it to execute on the else condition, you'll need to enclose everything from the block in brackets, eg:

Code:

if ( iNumber > 10 || iNumber < 1 ) 
{
        printf("Enter a number between 1 and 10");
}
else
{
        if (iNumber == iAnswer)
        {
		printf("\nYou guessed right!\n");
	}
        else
        {
		printf("\nSorry, you guessed wrong\n");
		printf("The correct guess was %d\n", iAnswer);
	}
}

EDIT: Ah, now I see isdigit is part of the requirements. In that case, declare a character and pass it to scanf with the %c format specifier.

**pmacdonald** · 07-11-2009

Thanks for the quick replies and clarifications. I had a hunch that I was using the isdigit function wrong.

**pmacdonald** · 07-11-2009

A few more questions arose. How do I correctly call char cResponse to see if it is equal to the integer iAnswer?

This code turned up many error in; srand, time, and rand.

Any ideas?

Code:

#include <stdio.h>
#include <ctype.h>

main()
{

    char cResponse = '\0';
    int iAnswer = 0;
    srand(time());

    iAnswer = (rand() % 10) + 1;

    printf("Guessing Game\n");
    printf("\nGuess a number from 1 to 10: ");
    scanf("%c", &cResponse);

    if isdigt(cResponse) > 10 || isdigit(cResponse) < 1
    {
        printf("Enter a number between 1 and 10");
    }
    else
    {
        if (cResposne == iAnswer)
        {
            printf("\nYou guessed right!\n");
        }
        else
        {
            printf("\nSorry, you guessed wrong\n");
            printf("The correct guess was %d\n", iAnswer);
        }
    }
}

**Elysia** · 07-11-2009

Must must return int.
Missing ( and ) around the if.

**Salem** · 07-11-2009

> if isdigt(cResponse) > 10 || isdigit(cResponse) < 1
isdigit() is a TRUE/FALSE deal.

isdigit('0') returns true (a non-zero result)
isdigit('A') returns false (zero)

**pmacdonald** · 07-11-2009

Please be more specific...around which if? I added them around the isdigit function and I still got the errors. I'm also not sure that I can compare the character to the integer so how would I do this yet still incorporate isdigit into the program?

Errors:
warning: return type default to 'int'
In function 'main':
warning: implicit declaration of function 'srand'
warning: implicit declaration of function 'time'
warning: implicit declaration of function 'rand'
error: syntax error before "isdigit"

**msh** · 07-11-2009

For starters, you're missing an include.

#include <stdlib.h>

That error is responsible for half your warnings.

**Elysia** · 07-11-2009

if isdigt(cResponse) > 10 || isdigit(cResponse) < 1
^ Missing ( and ).
EVERY if must begin with ( and end with ).
And as Salem points out, isdigit checks if the response is a digit or not. It doesn't check the range of a number, like if it's > 10.
Isdigit is like asking "is this a digit?" and it responds yes or no.

**pmacdonald** · 07-11-2009

msh - mmh, the book hasn't gone over that yet so there should be a way to make this program without incorporating it. I tried to add it but got the following errors:
warning: return type defaults to 'int'

In function 'main':
warning: implicit declaration of function 'time'
error: 'cResponse' undeclared (first sue in this function)
error: (Each undeclared identifier is reported only once

Elysia - I added the ( ) but still have errors.

So how do I incorporate isdigit into this program without having it compare numbers. As Elysia pointed out the function if isdigit(cResponse) > 10 || isdigit(cResponse) < 1 wouldn't even serve its pupose...correct?

**itCbitC** · 07-11-2009

Did you read Salems' post at all??

**msh** · 07-11-2009

Originally Posted by pmacdonald

msh - mmh, the book hasn't gone over that yet so there should be a way to make this program without incorporating it. I tried to add it but got the following errors:
warning: return type defaults to 'int'

In function 'main':
warning: implicit declaration of function 'time'
error: 'cResponse' undeclared (first sue in this function)
error: (Each undeclared identifier is reported only once

If the book has not covered stdlib.h yet you technically can't use srand() and rand() functions either.

Originally Posted by pmacdonald

So how do I incorporate isdigit into this program without having it compare numbers. As Elysia pointed out the function if isdigit(cResponse) > 10 || isdigit(cResponse) < 1 wouldn't even serve its pupose...correct?

You loop for input until the user gives you something that looks like a digit.

**Elysia** · 07-11-2009

Originally Posted by msh

You loop for input until the user gives you something that looks like a digit.

No, you make some pseudo code for what you want to do and translate it into real C code, whether or not that includes isdigit.
Beginners won't learn if you throw the spoon to them. They must learn to get it themselves.
In other words, don't tell them how to logically do something! They must use their own logic to come to this conclusion!
It's alright to explain functions do and introduce new functions to help with a specific task, but logic must never be handed out! This is a very critical part of programming and it is essential that every programmer out there knows it like the back of their hands!

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