How to correctly divide a number to only one digit in C?

Question

I have the following function :

divisibilidade11(int num);

And the following variables: :

int dividendo;
int divisor;

When the user enters with the type 11 for the variable divisor the function divisibilidade11 will be called and will check if the variable dividendo is divisible by divisor. And to check whether it is divisible or not, you will have to follow the criteria : If the sum of this even-order digit (Sp) subtracted from the odd-order sum (Si), results in 0 or a number divisible by 11, it returns true and if not, it returns false.

Example :

User enters with number 2376 for the variable dividendo;

User enters with number 11 for the variable divisor;

Is called the function divisibilidade11, to check whether or not it is divisible;

The sum of the impairments (Si) = 3+6 = 9;

Sum of pairs (Sp) = 2+7 = 9;

Si - Sp = 0; Therefore, 2376 is divisible by 11.

NOTE: The right-most digit is the odd-order first digit.

Example of how it would appear to the user :

The function divisibilidade11 you have to repeat the process until the result is a number with a digit. If this digit is 0, then the original number is divisible by 11.

Answer 1

Using Strings

Knowing that the maximum value for integers that most computers currently support is up to 19 digits, I will use a 20-digit string to perform this operation.

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

char divisibilidade11(long long int dividendo){
    char array_numerico[20] = "";
    int total_par = 0;
    int total_impar = 0;
    snprintf(array_numerico, 20, "%lld", dividendo);
    for(char iterador = strlen(array_numerico) - 1, par = 0; iterador >= 0; iterador -= 1){
        if(!par){
            total_impar += array_numerico[iterador] - 48;
            par = 1;
        }
        else{
            total_par += array_numerico[iterador] - 48;
            par = 0;
        }
    }
    if((total_par - total_impar) == 0 || ((total_par - total_impar) % 11 == 0)){
        return 1;
    }
    else{
        return 0;
    }
}

Using Decimal Mathematical Operations

char divisibilidade11(long long int dividendo){
    int total_par = 0;
    int total_impar = 0;
    char par = 0;
    while(dividendo != 0){
        if(!par){
            total_impar += (dividendo % 10);
            par = 1;
        }
        else{
            total_par += (dividendo % 10);
            par = 0;
        }
        dividendo /= 10;
    }
    if((total_par - total_impar) == 0 || (total_par - total_impar) % 11 == 0)
        return 1;
    else return 0;
}