Thread: A bit of an issue, converting char into int...

Hello you wonderful people...

I was wondering if I could get your help real quick please, and thank you...

So I want to write a code for an assignment to validate an ISBN number.

So once the user inputs the number, I need to take each digit and multiply it by a predetermined weight, but since I am using a string array for the input, I am having a bit of a problem. The program runs, but gives me the wrong results...

Can you please help me to figure out how to convert a char into int. I have used atoi, but that converts the entire input rather than digit by digit.

Thanks a bunch

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

main(void)
{
    char isbn[80];
    int len, n,  weight  ;
    int weighted_value;
    int counter=0;

    printf("please enter the ISBN number: ");
    scanf("%s", isbn);

    printf("the first number is %c\n", isbn[0]);
    printf("the second number is %c\n", isbn[1]);
    printf("the third number is %c\n", isbn[2]);
    printf("the fourth number is %c\n", isbn[3]);
    printf("the fifth number is %c\n", isbn[4]);
    printf("the sixth number is %c\n", isbn[5]);
    printf("the seventh number is %c\n", isbn[6]);
    printf("the eighth number is %c\n", isbn[7]);
    printf("the nineth number is %c\n", isbn[8]);
    printf("the tenth number is %c\n", isbn[9]);

    len = strlen(isbn);

    if (len <= 10)
    {
        printf("valid\n");
        //while (counter!=10)
            //{
                weight = 10;
   
                //HERE IS WHERE I NEED THE HELP, THANKS//

                n=atoi(isbn[0]);

                weighted_value=n*weight;

                printf("the n value for the first number is %d\n", n);


                printf("the weighted value for the first number is %d\n", weighted_value);
            //}
    }

}

Like this, if I understand your question correctly.

Code:

n  = (int)(isbn[counter] - '0');

ok so basically say I input the number "1234567890"

what I want to do is take 1 and multiply it by 10 and get a value

so I need to convert the input digit by digit into an int so I can multiply it by the predetermined weight that I will set in my code, in this case being 10

that worked perfectly... thank you so much

but just so I understand what you did, do you mind explaining the code to me? so I can learn and not just copy it? thank you so much

The individual digits in the character array are represented by their ascii ( or utf-8..whatever) values.
In the ascii table, the numbers are placed next to each other....so subtracting the character value of zero from the value of a single digit number, will give that number back.

sweet... thank you sir. Greatly appreciate it.