**FREE
Ctl-Opt Main(ThreeNPlusOne);

Dcl-Proc ThreeNPlusOne;
    Dcl-S n            Packed(10);
    Dcl-S counter      Int(10) Inz(0);
    Dcl-S input_prompt VarChar(50) Inz('Enter a positive integer (or 0 to exit):');

    // Use an infinite loop, exit when user enters 0
    Dow (1 = 1);
        Dsply input_prompt ' ' n;

        If n = 0;
            Leave;
        EndIf;

        If n < 0;
            input_prompt = 'Positive integers only. Enter a number:';
            Iter;
        EndIf;

        // Start sequence calculation
        input_prompt = 'Enter a positive integer (or 0 to exit):'; // Reset prompt
        counter = 0;
        Dsply ('Sequence for ' + %Char(n) + ':');

        Dow n > 1;
            If %Rem(n:2) = 0;
                // n is even, divide by 2
                n = n / 2;
            Else;
                // n is odd, multiply by 3 and add 1
                n = (n * 3) + 1;
            EndIf;

            counter = counter + 1;
            Dsply %Char(n);
        EndDo;

        Dsply ('Reached 1 in ' + %Char(counter) + ' iterations.');
        Dsply ' '; // Add a blank line for readability
    EndDo;

End-Proc ThreeNPlusOne;