Code for using terminal colors as with menus

#include <iostream>
#include <string>
#include <thread>
#include <chrono>
#include <fstream>
#include <vector>
#include <stdlib.h>


// Name space resolutions
using namespace std ;

//prototypes
void Menu(int &);

// Forward declare the slow_print function
void slow_print(string message , unsigned int);


// Main function
int main()
{
    int choice = 0;

    string filename ;
    string mystring ;





    Menu(choice) ;

    do
    {
    switch(choice)
            {
            case 1:

                    // begin block statement
                    {
                        // Due to the way that cin works we have to clear the input first
                        cin.clear();
                        cin.ignore(numeric_limits<streamsize>::max(), '\n');
                        // if we dont the above then prompt prints twice first time round

                        do{
                        cout <<"\nPlease enter name of file to read  or enter M to return to menu : " ;
                        getline(cin, filename);
                        }while (filename.length()==0) ;

                        if (filename.compare("M")!=0)
                        {




                                ifstream myfile(filename);
                                if(!myfile) //Always test the file open.
                                {
                                cout<<"Error opening file"<< endl;
                                return -1  ;
                                }

                                while (std::getline(myfile, mystring)) {
                                // output the line:


                                slow_print(mystring, 80);
                                }

                        myfile.close() ;

                        }

                        // for unix / linux systems only
                        system("clear");

                        break;
                    } //end block statements


            case 2:


                     break ;


            default:

                // for unix / linux systems only
                system("clear");
                cout << "\nInvalid input Please re enter " ;
            }

            // call menu again

            Menu(choice) ;


    }while(choice!=2)  ;


    cout << "Exiting  menu thankyou for using this  " << endl ;


    return (EXIT_SUCCESS) ;
}

// Implement the slow_print function
/**
 * Function to print each character in a string with a delay (a "typewriter" effect)
 * @param message         The string to print
 * @param millis_per_char Milliseconds to take to print each character
 */


void slow_print(string message, unsigned int millis_per_char)
{

    const std::string red("\033[0;31m");
    const std::string green("\033[1;32m");
    const std::string yellow("\033[1;33m");
    const std::string cyan("\033[0;36m");
    const std::string magenta("\033[0;35m");
    const std::string reset("\033[0m");


    // Range loops are "for each" constructs; here: for each character in the string
    for (const char c: message)
    {
        // flush is used to make sure the buffer is emptied to the terminal immediately
        cout << cyan << c << reset << flush;

        // Ask the thread to sleep for at least n millis.
        this_thread::sleep_for(std::chrono::milliseconds(millis_per_char));
    }
}

void Menu(int &choice)
    {
         cout << "\n    Choose an option:";
         cout << "\n...................................";
         cout << "\n 1- Instructions ";
         cout << "\n 2- Exit ";

         cout << "\n\nEnter your choice: ";
         cin >> choice ;
    }