Improving my C++ calculator u,u

#include <iostream>
#include <windows.h>

using namespace std;

int main()
{
restart_calculator:
system("mode 58, 23");
    char endChoice;
    do{
        system("cls");

        cout << "================\n C++ CALCULATOR\n================" << endl;

        //Input first number
        cout << "\n\n Choose the first number (use \".\" for decimals): " << endl;
        double firstNumber;
        cin >> firstNumber;

        //Input second number
        cout << "\n Now choose the second number (use \".\" for decimals): " << endl;
        double secondNumber;
        cin >> secondNumber;

        //Input operation
        cout << "\n Choose your operation ( +, -, * or / )" << endl;
        char operation;
        cin >> operation;

        //Case switch for operations
        switch(operation){
        case '+':
            {
                cout << "\n The result is: " << firstNumber + secondNumber << endl;
                break;
            }
        case '-':
            {
                cout << "\n The result is: " << firstNumber - secondNumber << endl;
                break;
            }
        case '*':
            {
                cout << "\n The result is: " << firstNumber * secondNumber << endl;
                break;
            }
        case '/':
            {
                cout << "\n The result is: " << firstNumber / secondNumber << endl;
                break;
            }
        default:
            {
                cout << "\n Please, next time, choose a valid operation!" << endl;
            }
        }

        cout << "\n\n--------------------------\nDeveloped by Wolfiy\n" << "\nMake another calcul? [Y/N]" << endl;

        //End Switch

        restart_ask:
        cin >> endChoice;
        switch(endChoice){
        case 'N': case 'n':
            {
                exit(0);
            }
        case 'Y': case 'y':
            {
                continue;
            }
        default:
            {
                do{
                    cout << "\n Please, select between Y (yes) and N (no)." << endl;
                    cin >> endChoice;
                    if(endChoice == 'N' || 'n'){
                        exit(0);
                    }
                    else if(endChoice == 'Y' || 'y'){
                        goto restart_calculator;
                    }
                    else{
                        goto restart_ask;
                    }

                }while(endChoice != 'Y' || 'y' || 'N' || 'n');
            }
        }

    }while(endChoice == 'Y', 'y');

        return 0;
}