Длинное сложение/вычитание

#include <iostream>
#include<string>
using namespace std;

char data_in(const int max_size, int* arr) {
    string s;
    cin >> s;
    char sign = '+';

    int i = 0;
    int len;
    len = s.length();
    if (s[0] == '-') {
        s.erase(0, 1);
        len--;
        sign = '-';
    }

    for (int i = 0; i < max_size; ++i)
        arr[i] = 0;

    for (i; i < len; i++)
        arr[len - i] = int(s[i]) - 48;

    return sign;
}

void data_out(const int max_size, int* arr, char sign) {
    int i = max_size - 1, sum = 0;
    while (arr[i] == 0 && i >= 0) i--;

    if (i == -1) {
        cout << 0;
        return;
    }

    if (sign == '-') {
        cout << '-';
        for (int j = i; j >= 1; j--)
            cout << arr[j];
    }
    else {
        for (int j = i; j >= 1; j--)
            cout << arr[j];
    }

}

int what_is_bigger(const int max_size, int* arr1, int* arr2) {
    int i, num_max = 1;

    for (i = max_size; i >= 0; i--) {
        if (((arr1[i] != 0) || (arr2[i] != 0)) && (arr1[i] > arr2[i])) {
            num_max = 1;
            break;
        }
        if (((arr1[i] != 0) || (arr2[i] != 0)) && (arr1[i] < arr2[i])) {
            num_max = 2;
            break;
        }
    }

    return num_max;
}

void long_plus(const int max_size, int* arr1, int* arr2) {
    int c = 0;
    for (int i = 1; i < max_size; ++i) {
        c = c + arr1[i] + arr2[i];
        arr1[i] = c % 10;
        c /= 10;
    }
}

void long_minus(const int max_size, int* arr1, int* arr2) {
    int i, c = 0;
    for (i = 0; i < max_size; i++) {
        arr1[i] = arr1[i] - arr2[i] + c;
        c = 0;
        if (arr1[i] < 0) {
            arr1[i] += 10;
            c--;
        }
    }
}

void operation_def(const int max_size, int* arr1, int* arr2, char signa, char signb, char operation) {
    char sign = '+';
    int num_max;
    num_max = what_is_bigger(max_size, arr1, arr2);

    if (operation == '+') {
        if (signa == signb) {
            long_plus(max_size, arr1, arr2);

            if (signa == '+') sign = '+';
            if (signa == '-') sign = '-';

            data_out(max_size, arr1, sign);
        }
        else {
            if (signa == '+') {
                if (num_max == 1) {
                    sign = '+';
                    long_minus(max_size, arr1, arr2);
                    data_out(max_size, arr1, sign);
                }
                else {
                    sign = '-';
                    long_minus(max_size, arr2, arr1);
                    data_out(max_size, arr2, sign);
                }
            }
            else {
                if (num_max == 1) {
                    sign = '-';
                    long_minus(max_size, arr1, arr2);
                    data_out(max_size, arr1, sign);
                }
                else {
                    sign = '+';
                    long_minus(max_size, arr2, arr1);
                    data_out(max_size, arr2, sign);
                }
            }
        }
    }

    if (operation == '-') {
        if (signa == signb) {
            if (signa == '+') {
                if (num_max == 1) {
                    sign = '+';
                    long_minus(max_size, arr1, arr2);
                    data_out(max_size, arr1, sign);
                }
                else {
                    sign = '-';
                    long_minus(max_size, arr2, arr1);
                    data_out(max_size, arr2, sign);
                }
            }
            else {
                if (num_max == 1) {
                    sign = '-';
                    long_minus(max_size, arr1, arr2);
                    data_out(max_size, arr1, sign);
                }
                else {
                    sign = '+';
                    long_minus(max_size, arr2, arr1);
                    data_out(max_size, arr2, sign);
                }
            }
        }
        else {
            long_plus(max_size, arr1, arr2);

            if (signa == '+') sign = '+';
            if (signa == '-') sign = '-';

            data_out(max_size, arr1, sign);
        }
    }
}

int main()
{
    const int max_size = 100000;
    char operation;
    char signa = '+', signb = '+';
    int i = 0, sum = 0;
    int* a = new int[max_size];
    int* b = new int[max_size];


    signa = data_in(max_size, a);
    cin >> operation;
    signb = data_in(max_size, b);

    operation_def(max_size, a, b, signa, signb, operation);

    delete a;
    delete b;
}