I need help with my assignement

[JustAProgrammer]

Write a program for a banking system.The program shoudl allow 3 users to login to their account using a username and a password,then display a menu to allow a user to do the following :
Deposit into account
Withdraw from account
Display balance
Add interest
Exit

So this is what I wrote

#include <iostream>

Using namespace std ;

Int main()
{
string username1=john , password1=1234 ;

double balance=0 ,interest = 0.15 ;

int counter ;

counter =counter+1 ;

cout << "Enter a username" ;

cin >> username1 ;

cout << "Enter password" ;

cin >> password1 ;