macro do loop and recursive method

[pavank]

Hi Everyone

Goodmornin

macro function %countdown having a numeric parameter and producing the following output in the log :

Countdown 10...

Countdown 9...

Countdown 8...

Countdown 7...

Countdown 6...

Countdown 5...

Countdown 4...

Countdown 3...

Countdown 2...

Countdown 1...

BOOM !!!

1. Using a %do loop
2. Using a recursive method

[Kurt_Bremser]

From the lessons in your course, you should be able to do your homework yourself.

Let us see what you tried.

[pavank]

data count;

var='countdown';
do i=n to 1 by -1;

put vari;
end;
stop;
run;

Could you please give solution

[Kurt_Bremser]

So next, do the same in a macro with a %DO loop and a macro parameter as starting value.

[pavank]

I didn't get any  idea how to do that 

[Kurt_Bremser]

Were you sleeping through the course lessons?

Converting a data step loop to a macro loop is dead simple (if you paid any attention).

[pavank]

%macro countdown(ds,num);
var='Countdown';
%do i= 10 %to  1 by -1;
output;
end;
stop;
put vari;
run;
%macro;

%countdown(ds,10);
%put(countdown.. &i);

I didn't get output ??

[Kurt_Bremser · Accepted solution]

%macro countdown(num);
%do i = &num. %to 1 %by -1;
  %put Countdown &i.;
%end;
%put Boom!;
%mend;

%countdown(10);

Study this closely, so you get a grasp on the very basics of macro programming.

Next, go searching for the concept of recursion in programming, and see how you can apply it to this task.

[pavank]

THANK YOU VERY MUCH 

 KurtBremser

[Tom]

There is no recursion in that example.

[pavank]

What is recursive method how to do recursive methof using bu above example

[Tom]

Here is an introduction to the concept of recursion.

https://www.topcoder.com/thrive/articles/An%20Introduction%20to%20Recursion%20Part%20One

The SAS solution for your problems looks very much like the first example.

%macro countdown(start);
%if &start > 0 %then %do;
  %put Countdown &start;
  %countdown(%eval(&start-1))
%end;
%else %put BOOM !!!;
%mend countdown;

[David_Billa]

Why by -1 in do loop?

[PaigeMiller]

---

@David_Billa wrote:
Why by -1 in do loop?

---

If you want a loop to go from 10 to 9 to 8 to ..., what is the increment that gets you from 10 to 9?

[Kurt_Bremser]

Because it's a countdown.