LAB3.0 (new)

#include <iostream>

using namespace std;

int Task1(int a, int n);
int Task2(int a);
double Task3(float n, double& result);
int Task4(int n, int k);
int Task5(int n, int k);
int Task6(int a, int& n);
int Task7(int n);
int Task10(int n);
int Task11F(int n);
int Task11G(int n);
int Task12F(int n);
int Task12G(int n);
void Task13(int n, int& F, int& G);
int Task15(int k);

int main()
{
    int choice = 0, exit = 0;
    do {
        cout << "Enter from 1 to 12 to choose task or 0 to exit: "; cin >> choice;
        if (choice == 0) exit = 1;
        else if (choice == 1) {
            int a, n;
            cout << "Enter 'a': "; cin >> a;
            cout << "Enter 'n': "; cin >> n;
            if (n > 0)
                cout << "Result: " << Task1(a, n) << endl;
            else
                cout << "Incorrect data..." << endl;

        }
        else if (choice == 2) {
            int a;
            cout << "Enter 'a': "; cin >> a;
            if (a >= 0)
                cout << "Result: " << Task2(a) << endl;
            else
                cout << "Incorrect data..." << endl;
        }
        else if (choice == 3) {
            double result = 1;
            float n;
            cout << "Enter 'n': "; cin >> n;
            if (n >= 0)
                cout << "Result: " << Task3(n, result) << endl;
            else
                cout << "Incorrect data..." << endl;
            result = 0;
        }
        else if (choice == 4) {
            int n, k;
            cout << "Enter k (k <= n): "; cin >> k;
            cout << "Enter n (n >= k): "; cin >> n;
            if (k > n || k < 0 || n < 0)
                cout << "Incorrect data..." << endl;
            else
                cout << "C(" << n << ", " << k << "): " << Task4(n, k) << endl;
        }
        else if (choice == 5) {
            int n, k;
            do {
                cout << "Enter 'n': "; cin >> n;
                cout << "Enter 'k': "; cin >> k;
            } while (k < 0 && n < 0);
            cout << "Result: " << Task5(n, k) << endl;
        }
        else if (choice == 6) {
            int a, n;
            cout << "Enter 'a': "; cin >> a;
            cout << "Count: " << Task6(a, n) << endl;
            cout << "Max: " << n << endl;
        }
        else if (choice == 7) {
            int n;
            cout << "Enter 'n': "; cin >> n;
            if (n > 0)
                cout << "Result: " << Task7(n) << endl;
            else
                cout << "Incorrect data..." << endl;
        }
        else if (choice == 8) {
            cout << "Contact me: mempron@outlook.com; to ask done this one";
        }
        else if (choice == 9) {
            cout << "Contact me: mempron@outlook.com; to ask done this one";
        }
        else if (choice == 10) {
            int n = 0;
            cout << "Enter 'n': "; cin >> n;
            cout << "Result: " << Task10(n) << endl;
        }
        else if (choice == 11) {
            int n = 0;
            cout << "Enter 'n': "; cin >> n;

            cout << "Result: " << Task11F(n) + Task11G(n) << endl;
        }
        else if (choice == 12) {
            int n = 0;
            cout << "Enter 'n': "; cin >> n;
            cout << "Result: " << Task12F(n) + Task12G(n) << endl;
        }
        else if (choice == 13) {
            int n = 0, F = 1, G = 1;
            cout << "Enter 'n': "; cin >> n;
            Task13(n, F, G);
            cout << "Result: " << F / G << endl;
        }
        else if (choice == 14) {
            cout << "Contact me: mempron@outlook.com; to ask done this one";
        }
        else if (choice == 15) {
            int n, k;
            cout << "Enter 'a': "; cin >> n;
            cout << "Enter 'n': "; cin >> k;
            if (k > 0)
                cout << "Result: " << n + Task15(k) << endl;
            else
                cout << "Incorrect data..." << endl;
        }
        else cout << "Incorrect data..." << endl;
    } while (!exit);
}

int Task1(int a, int n) {
    if (n == 0) return 1;
    else if (n == 1) return a;
    return a * Task1(a, n - 1);
}
int Task2(int a) {
    if (a == 0) return 1;
    return a * Task2(a - 1);
}
double Task3(float n, double &result) {
    int fact = Task2(n);
    if (n == 0)
        return 1;
    return Task3(n - 1, result) + (1. / fact);
}
int Task4(int n, int k) {
    if (k == 0 || k == n)
        return 1;
    else
        return Task4(n - 1, k) + Task4(n - 1, k - 1);
}
int Task5(int n, int k) {
    if (k == 1) return n;
    return n + Task5(n, k - 1);
}
int Task6(int a, int& n) {
    if (n <= a % 10) n = a % 10;
    if (a >= 0 && a <= 9) return 1;
    else return Task6(a / 10, n) + 1;
}
int Task7(int n) {
    if (n == 0) return 0;
    if (n == 1) return 1;
    return Task7(n - 1) + Task7(n - 2);
}
int Task10(int n) {
    if (n == 1) return 3;
    return Task10(n - 1) * (n - 1);
}
int Task11F(int n) {
    if (n == 0) return 0;
    return Task11F(n - 1) + n;
}
int Task11G(int n) {
    if (n == 1) return 1;
    return Task11G(n - 1) * n;
}
int Task12F(int n) {
    if (n == 1) return 1;
    return 2 * Task12G(n - 1) + 5 * n;
}
int Task12G(int n) {
    if (n == 1) return 1;
    return Task12F(n - 1) + 2 * n;
}
void Task13(int n, int& F, int& G) {
    if (n == 1) {
        F = 1;
        G = 1;
        return;
    }
    int F1 = G;
    F = F - G;
    G = F1 + G;
    Task13(n - 1, G, F);
}
int Task15(int k) {
    if (k == 1)
        return 1;
    return 1 + Task15(k - 1);
}