Arithmetic with a string.

I have a string "I10014" stored as a char, I need to do arithmetic on each of the numbers individually i.e. 1 * 5, so that I have a result for each sum and then add them all up to have a total. But I want to do it in a function, so will need to pass the string to it.
Please help.;)

You can change a character to the number equivalent by subtracting '0'.

Code:

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#include <stdio.h>

add(char *nums){
    int sum=0;

    if (*nums=='A'){
        while (*++nums!='\0')
            sum+=*nums-'0';
        printf("The total is %d\n", sum);
    }
}

main(){
    char b[]="A10014";

    add(b);
}

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