Some task

#include <iostream>

#include <cmath>

#define N 1000

using namespace std;

class InfNum {

    public:

        int to_int() {
            int res = 0;

            for (int i = N - 1; i >= 0; i--) {
                res += (*this).data[i] * pow(10, N - 1 - i);
            }

            if (sign == -1) {
                res *= -1;
            }

            return res;
        }

        InfNum operator + (InfNum & num) {
            int this_sign = this -> sign, num_sign = num.sign;

            InfNum result = sum_sign(*this, num);

            this -> sign = this_sign;
            num.sign = num_sign;

            return result;
        }

        InfNum operator - (InfNum & num) {
            int this_sign = this -> sign, num_sign = num.sign;

            InfNum result = diff_sign(*this, num);

            this -> sign = this_sign;
            num.sign = num_sign;

            return result;
        }

        InfNum operator * (InfNum & num) {
            int this_sign = this -> sign, num_sign = num.sign;

            InfNum result = mult_sign(*this, num);

            this -> sign = this_sign;
            num.sign = num_sign;

            return result;
        }

        InfNum operator / (InfNum & num) {
            int this_sign = this -> sign, num_sign = num.sign;

            InfNum result = div_sign(*this, num);

            this -> sign = this_sign;
            num.sign = num_sign;

            return result;
        }

        char in () {
            string s;

            cin >> s;

            set(s);

            return ' ';
        }

        void set(string s) {
            * this = init();

            int i = 0;

            if (s[0] == '-') {
                i++;

                sign = -1;
            } else {
                sign = 1;
            }

            for (i; i < s.size(); i++) {
                data[N - s.size() + i] = s[i] - '0';
            }
        }

        char out() {
            if (sign == -1) {
                cout << "-";
            }

            bool flag = false;

            for (int i = 0; i < N; i++) {
                if (data[i] != 0) {
                    flag = true;
                }

                if (flag) {
                    cout << data[i];
                }
            }

            if (!flag) {
                cout << "0";
            }

            return ' ';
        }

    private:

        int sign = 1;
        int data[N] = {
            0
        };

        bool isZero(InfNum & num) {
            for (int i = N - 1; i >= 0; i--) {
                if (num.data[i] != 0) {
                    return false;
                }
            }

            return true;
        }

        void div_by_int(InfNum & num, int int_num) {
            for (int i = 0; i < N; i++) {
                if (i + 1 < N) {
                    num.data[i + 1] += (num.data[i] % int_num) * 10;
                }

                num.data[i] /= int_num;
            }
        }

        void fix_sign(InfNum & num) {
            if (isZero(num) == true) {
                num.sign = 1;
            }
        }

        void swap(InfNum & a, InfNum & b) {
            InfNum c = a;

            a = b;
            b = c;
        }

        int compare(InfNum & a, InfNum & b) {
            if (a.sign > b.sign) {
                return 1;
            }
            if (a.sign < b.sign) {
                return -1;
            }

            for (int i = 0; i < N; i++) {
                if (a.data[i] > b.data[i]) {
                    return a.sign;
                } else if (a.data[i] < b.data[i]) {
                    return -1 * a.sign;
                }
            }

            return 0;
        }

        InfNum sum(InfNum & a, InfNum & b) {
            InfNum c;

            for (int i = N - 1; i >= 0; i--) {
                c.data[i] = a.data[i] + b.data[i];
            }

            fix_system(c);

            return c;
        }

        InfNum diff(InfNum & a, InfNum & b) {
            InfNum c;

            for (int i = N - 1; i >= 0; i--) {
                c.data[i] = a.data[i] - b.data[i];
            }

            fix_system(c);

            return c;
        }

        void fix_system(InfNum & num) {
            for (int i = N - 1; i >= 0; i--) {
                if (i > 0) {
                    if (num.data[i] > 9) {
                        num.data[i - 1] += num.data[i] / 10;
                        num.data[i] = num.data[i] % 10;
                    }
                    if (num.data[i] < 0) {
                        while (num.data[i] < 0) {
                            num.data[i] += 10;
                            num.data[i - 1] -= 1;
                        }
                    }
                }
            }
        }

        InfNum mult(InfNum & a, InfNum & b) {
            InfNum c;

            for (int i = N - 1; i >= 0; i--) {
                InfNum temp;

                for (int j = N - 1; j >= 0; j--) {
                    if (N - 1 - (N - 1 - i + N - 1 - j) >= 0) {
                        temp.data[N - 1 - (N - 1 - i + N - 1 - j)] += a.data[i] * b.data[j];
                    }
                }

                c = c + temp;
            }

            fix_system(c);

            return c;
        }

        InfNum div(InfNum & a, InfNum & b) {
            InfNum c;

            int cmp = compare(a, b);

            if (cmp == -1) {
                return init();
            }
            if (cmp == 0) {
                c.set("1");

                return c;
            }

            if (isZero(a) == true) {
                return init();
            }

            if (isZero(b) == true) {
                return init();
            }

            InfNum t;

            t.set("1");

            if (compare(b, t) == 0) {
                return a;
            }

            InfNum r_b, l_b;

            l_b.set("1");
            r_b = a;

            InfNum prev_c = init();

            do {
                prev_c = c;

                c = r_b + l_b;

                div_by_int(c, 2);

                InfNum res;

                res = b * c;

                cmp = compare(a, res);

                if (cmp == 1) {
                    l_b = c;
                }
                if (cmp == -1) {
                    r_b = c;
                }
            } while (cmp != 0 && compare(c, prev_c) != 0);

            return c;
        }

        InfNum sum_sign(InfNum & a, InfNum & b) {
            InfNum c;
            bool swap_flag = false;

            if (a.sign == b.sign) {
                c = sum(a, b);

                c.sign = a.sign;

                fix_sign(c);

                return c;
            } else {

                if (b.sign == 1) {
                    swap(a, b);

                    swap_flag = true;
                }

                b.sign = 1;

                int cmp = compare(a, b);

                if (cmp != -1) {
                    c = diff(a, b);
                } else {
                    c = diff(b, a);

                    c.sign = -1;
                }
            }

            fix_sign(c);

            if (swap_flag == true) {
                swap(a, b);
            }

            return c;
        }

        InfNum diff_sign(InfNum & a, InfNum & b) {
            InfNum c;

            if (a.sign != b.sign) {
                c = sum(a, b);

                c.sign = a.sign;

                if (isZero(c) == true) {
                    c.sign = 1;
                }

                fix_sign(c);

                return c;
            } else {

                b.sign *= -1;

                if (isZero(c) == true) {
                    c.sign = 1;
                }

                return sum_sign(a, b);
            }

            return c;
        }

        InfNum mult_sign(InfNum & a, InfNum & b) {
            InfNum c = mult(a, b);

            c.sign = (a.sign * b.sign);

            return c;
        }

        InfNum div_sign(InfNum & a, InfNum & b) {
            int c_sign = a.sign * b.sign;

            a.sign = b.sign = 1;

            InfNum c = div(a, b);

            if (isZero(c) == false) {
                c.sign = c_sign;
            }

            return c;
        }

        InfNum init() {
            InfNum num;

            return num;
        }
};

int main() {

    InfNum a, b, c;

    cout << "Enter num a: " << a.in() << endl;

    cout << "Enter num b: " << b.in() << endl;

    c = a + b;

    cout << "a + b = " << c.out() << endl;

    //

    c = a - b;

    cout << "a - b = " << c.out() << endl;

    //

    c = a * b;

    cout << "a * b = " << c.out() << endl;

    //

    c = a / b;

    cout << "a / b = " << c.out() << endl;

    return 0;
}