Colloquium_4_task_3

int adder(const string_t s)
{
    int i = 0;
    int len = 0;
    int number = 0;
    int rank = 1;
    int n = 0;
    int sum = 0;

    while (s[i])
    {
        i++;
        len++;
    }

    for (i = len-1; i >= 0; i--)
    {
        if (s[i] != '+' && s[i] != '-')
        {
            printf("\n*%d\n", (int)(s[i] - '0') * rank);
            number += (int)(s[i] - '0') * rank;
            rank *= 10;
        }

        else
        {
            if (s[i] == '+')
                sum += number;
            else
                sum -= number;
            rank = 1;
            number = 0;
        }
    }

    if (s[len-1] != '+' && s[len-1] != '-')
        sum += number;

    return sum;
}