#include <stdlib.h>
#include <locale.h>
#include <iostream>
#include <string>
#include <cmath>

using namespace std;

// todo think of removing unnecessary zeroes in the beginning of the num

bool validNumForDouble(string num) {
    int countOfComma = 0;
    for (char ch : num) {
        if (ch == '.' || to_string(ch) == to_string(',')) {
            cout << "check " << endl;
            countOfComma++;
        }
    }

    return countOfComma <= 1;
}

bool numIsValid(string num) {
    bool hasDigit = false;
    bool metPoints = false;

    if (num.length() == 0 || num[0] < '0' || num[0] > '9' ) return false;

    for (char c : num) {
        if (c >= '0' && c <= '9') {
            hasDigit = true;
        } else if (c == '.' || c == ',') {
            if (metPoints) return false;
            metPoints = true;
        }
        else return false;
    }

    if (!hasDigit) {
        return false;
    }

    return true;
}

bool isPositive(string num) {
    if (num[0] == '-') {
        return false;
    } else if (num[0] == '+') {
        return true;
    } else if (num[0] >= '0' && num[0] <= '9') {
        return true;
    }

    return false;
}

void sum() {
    string firstNum;
    string secondNum;

    while(true) {
        cout << endl << "First num: ";
        cin >> firstNum;
        if(!numIsValid(firstNum)) {
            cout << "Num is not valid";
        } else break;
    }

    while(true) {
        cout << endl << "Second num: ";
        cin >> secondNum;
        if(!numIsValid(secondNum)) {
            cout << "Num is not valid";
        } else break;
    }

    cout << firstNum << " + " << secondNum << " = " << stol(firstNum) + stol(secondNum);

    cout << endl;
    system("pause");
}

void substract() {
    string firstNum;
    string secondNum;

    while(true) {
        cout << endl << "First num: ";
        cin >> firstNum;
        if(!validNumForDouble(firstNum)) {
            cout << "Num is not valid";
        } else break;
    }

    while(true) {
        cout << endl << "Second num: ";
        cin >> secondNum;
        if(!validNumForDouble(secondNum)) {
            cout << "Num is not valid";
        } else break;
    }

    cout << firstNum << " - " << secondNum << " = " << stol(firstNum) - stol(secondNum);

    cout << endl;
    system("pause");
}
void multiply() {
    string firstNum;
    string secondNum;

    while(true) {
        cout << endl << "First num: ";
        cin >> firstNum;
        if(!validNumForDouble(firstNum)) {
            cout << "Num is not valid";
        } else break;
    }

    while(true) {
        cout << endl << "Second num: ";
        cin >> secondNum;
        if(!validNumForDouble(secondNum)) {
            cout << "Num is not valid";
        } else break;
    }

    cout << firstNum << " * " << secondNum << " = " << stol(firstNum) * stol(secondNum);

    cout << endl;
    system("pause");
}

// todo check for zero
void divide() {
    string firstNum;
    string secondNum;

    while(true) {
        cout << endl << "First num: ";
        cin >> firstNum;
        if(!validNumForDouble(firstNum)) {
            cout << "Num is not valid";
        } else break;
    }

    while(true) {
        cout << endl << "Second num: ";
        cin >> secondNum;
        if(!validNumForDouble(secondNum)) {
            cout << "Num is not valid";
        } else break;
    }

    cout << firstNum << " / " << secondNum << " = " << stol(firstNum) / stol(secondNum);

    cout << endl;
    system("pause");
 }

void pow() {
    string firstNum;
    string extent;

    while(true) {
        cout << endl << "First num: ";
        cin >> firstNum;
        if(!validNumForDouble(firstNum)) {
            cout << "Num is not valid";
        } else break;
    }

    while(true) {
        cout << endl << "Extent: ";
        cin >> extent;
        if(!validNumForDouble(extent)) {
            cout << "Num is not valid";
        } else break;
    }

    cout << firstNum << " ^ " << extent << " = " << pow(stol(firstNum), stol(extent));

    cout << endl;
    system("pause");
 }

int main() {

    int menuItem = -1;

    bool isExit = false;
    while(!isExit) {
        cout
            << "\n 0 - Exit"
            << "\n 1 - Sum"
            << "\n 2 - Subsctract"
            << "\n 3 - Miltiply"
            << "\n 4 - Divide"
            << "\n 5 - Pow: ";

        cin >> menuItem;
        if(menuItem < 0 || menuItem > 5) continue;

        switch(menuItem) {
            case 0: isExit = true; break;
            case 1: sum(); break;
            case 2: substract(); break;
            case 3: multiply(); break;
            case 4: divide(); break;
            case 5: pow(); break;
            default: cout << "Menu item " << menuItem << " cannot be found";
        }
    }

    return 0;
}