Answer to Question #35711 in C++ for Arjay

Question

How to code this:
Duplicate Terminator
Create a program that will display all unique input from the user. If the entered number is
already entered, “has already been entered” then display the previous list of numbers.
Continue process until the user enters -1 to end the program.
Sample Input/Output:
Enter number: 5
5
Enter number: 9
5 9
Enter number: 2
5 9 2
Enter number: 9
9 has already been entered
5 9 2
Enter number: 1
5 9 2 1