stack

#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

vector<int> mystack;
int top = -1;
bool loaded = false;

void menu();
void push(int data);

void showStack()
{
    cout << "stekas: {";
    for(int i = 0; i <= top; i++)
    {
        if(i != top)
        {
            cout << mystack[i] << ", ";
        }
        else
        {
            cout << mystack[i] << "}" << endl;
        }
    }
}

void write()
{
    ofstream output("input.txt");
    int i = 0;
    while(i <= top)
    {
        output << mystack[i] << " ";
        i++;
    }
    output.close();
}

void read()
{
    ifstream input;
    input.open("input.txt");
    int data;
    while(input >> data)
    {
        push(data);
    }
    loaded = true;
    input.close();
}

bool isEmpty()
{
    if(top == -1)
    {
        return true;
    }
    else
    {
        return false;
    }
}

void pop()
{
    int data;
    if(!isEmpty())
    {
        data = mystack[top];
        mystack.pop_back();
        top = top - 1;
        cout << "--------" << endl;
        cout << data << " pasalintas is steko!" << endl;
        cout << "--------" << endl;
        cout << endl;
        menu();
    }
    else
    {
        cout << "--------" << endl;
        cout << "Stekas tuscias, nera ka pasalinti!" << endl;
        cout << "--------" << endl;
        cout << endl;
        menu();
    }
}

void push(int data)
{
    if(loaded == true)
    {
        top = top + 1;
        mystack.push_back(data);
        cout << "--------" << endl;
        cout << "Reiksme " << data << " iterpta i steka!" << endl;
        cout << "--------" << endl;
        cout << endl;
        menu();
    }
    else if(loaded == false)
    {
        top = top + 1;
        mystack.push_back(data);
    }
}

void menu()
{
    if(!isEmpty())
    {
        showStack();
    }
    else
    {
        cout << "stekas tuscias!" << endl;
    }

    cout << "---------------------------" << endl;
    cout << "1. Iterpti i steka (push)" << endl;
    cout << "2. Pasalinti is steko (pop)" << endl;
    cout << "3. Issaugoti steka" << endl;
    cout << "4. Issaugoti steka ir uzdaryti programa" << endl;
    cout << "---------------------------" << endl;
    cout << "Jusu pasirinkimas: ";

    char key;
    cin >> key;
    switch(key)
    {
        case '1':
        {
            cout << "Irasykite reiksme i konsole: ";
            int data;
            cin >> data;
            cout << endl;
            push(data);
            break;
        }
        case '2':
        {
            cout << endl;
            pop();
            break;
        }
        case '3':
        {
            write();
            cout << "--------" << endl;
            cout << "Stekas issaugotas!" << endl;
            cout << "--------" << endl;
            menu();
            break;
        }
        case '4':
        {
            write();
            break;
        }
        default:
        {
            cout << "Tokio pasirinkimo nera!" << endl;
            cout << endl;
            key = '\0';
            menu();
            break;
        }
    }
}

int main()
{
    read();
    menu();
    return 0;
}