Change/Keep Values (C beginner)

**Erazz** · 10-11-2014

Hey guys i'm new to C and i've got a little problem.

I would like to write a program that gives you a few default values. Now you can keep these values by pressing the enter key or you can change them by just typing in new ones and confirm the new values by pressing the enter key again.

Thats as far as i got on my own but it doesn't really work. I would appreciate it if one of you guys could tell what i can do to fix this.

Code:

#include<stdio.h>
#include <conio.h>

int getInt(int min, int max);

int main ()
{
    int a[3] = {3,4};
    int b;
    int code;
    int loop;

    for (b = 0 ; b < 2 ; b++){
        printf ("a[%d] = ",b);
    
        do{
            code = _getch();

            switch (code){
            case 13:
                printf("%d\n", a[b]);
                loop = 1;
                break;

            default:
                a[b] = getInt(0,6);
                loop = 1;
                break;
            }

        }while (loop != 1);
    }
}


int getInt(int min, int max)
{
    int num;        
    char ch;        
    int error = 1;     

    do    {
        
        fflush(stdin);

        //Error if you enter a character
        if (scanf("%d%c", &num, &ch) != 2)
        {
            printf("Error you entered a character\n");
        }

        //Error if you enter an incorect value
        else if ((ch != 10) || (num > max) || (num < min))    //
        {
            printf("Error, inncorect range of values\n");
        }

        //No Error, exit loop
        else
        {
            error = 0;
        }

    } while (error == 1);

    return num;
}

**c99tutorial** · 10-11-2014

Originally Posted by Erazz

Now you can keep these values by pressing the enter key or you can change them by just typing in new ones and confirm the new values by pressing the enter key again.

Thats as far as i got on my own but it doesn't really work.

If you want to allow user to press ENTER alone, then you need line-based input. I.e. use fgets to read a line into a buffer, and then use sscanf on that buffer just as you would use scanf. The way you're doing it now with scanf on its own, you can never catch the "user pressed ENTER" event.

If user presses enter then you could probably assign the default value within your getInt function.

Also note fflush(stdin) is not correct.

**Matticus** · 10-11-2014

You should tell us exactly what you mean by "doesn't really work". What input are you giving it? What output do you expect? What output are you actually getting?

Some additional comments:

Don't flush stdin: FAQ > Why fflush(stdin) is wrong - Cprogramming.com
Some alternatives here: FAQ > Flush the input buffer - Cprogramming.com

conio.h is old and non-standard; you can use "getchar()" instead

Avoid constants when checking for characters:

Code:

// instead of this:
case 13:

// use this:
case '\n':

// note that 13 is actually '\r', but you should check for '\n' as indicated

Code:

// instead of this:
(ch != 10)

// use this:
(ch != '\n')

Your use of arrays is a bit strange. You declare the array to have 3 elements, but you're only using two. And instead of magic numbers, you should #define a constant and use this instead. Not only does this increase readability, but if you want to expand the size of the array (and resulting code), you only have to change one value in your code, instead of hunting down all instances and changing each and every one (possibly missing some, leading to potential bugs).

Code:

#define MAX_SIZE 3

// ...

int array[MAX_SIZE] = ...

// ...

for(i=0; i<MAX_SIZE; i++)
    // ...

Also, use prompts in your program so the user knows what they're supposed to be entering.

And maybe you should print the array after the loop ends to see the final results.

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