Do loop until end?

[Myurathan]

I am new to sas. I am trying to run following code. It runs for ever. What am I doing wrong? I am tryting to see how many years it takes to payback loan.

data loan;
	initial_payment=1000;
	loan=30000-initial_payment;
	payment=500;
	years=0;

	do until (loan_end=0);
		years+1;
		loan_end=loan-payment;
	end;
run;

Thanks in advance.

run;

[Shmuel]

Try:

data loan;
	initial_payment=1000;
	loan=30000-initial_payment;
	payment=500;
	years=0;

	do until (loan_end LE 0);
		years+1;
		loan_end=loan-payment;
	end;
run;

[Myurathan]

Thanks @Shmuel. but it also runs forever. 😞

[RW9]

Why do you need the loop, it is a simple calculation:

data loan;
   initial_payment=1000;
   loan=30000-initial_payment;
   payment=500;
   years=loan / payment;
run;

As for why it does not work, well, your condition loan_end le 0 must never be true.

[Myurathan]

Thanks RW9. I am aware that it is a simple calulation. I am trying to learn looping. Can you please explain why loan_end le 0 never be true?. Thanks

[RW9 · Accepted solution]

In @Shmuel's example the value of loan_end is always loan-payment, 28500, hence it never lowers down to 0 or less.  Update this to :

data loan;
   initial_payment=1000;
   loan=30000-initial_payment;
   payment=500;
   years=0;
   loan_end=loan;
   do until (loan_end le 0);
      years+1;
      loan_end=loan_end-payment;
   end;
run;

So we set loan_end to be loan, then take payment off loan_end each time, so loan_end goes down  We could alos write it as:

data loan;
   initial_payment=1000;
   loan=30000-initial_payment;
   payment=500;
   years=0;
   do until (loan le 0);
      years+1;
      loan=loan-payment;
   end;
run;

Basically you need to ensure the condition in the until is triggered, which as it was being created each round never happened.

[Myurathan]

Thank you so much @RW9