SRL Archive - C/C++ Help and Tutorials

If you follow the link below it is the assignment I have to do.

http://staffwww.fullcoll.edu/sedwards/CS133/Announce/Announce.html#HW02_Rabbits

Rabbit (n) = (1 if n is 1 or 2) OR [Rabbit(n-1) + Rabbit(n-2); if n > 2]


The book gives this for an example code:

int rabbit(int n) {
  if (n <= 2) 
    return 1;
  else 
    return rabbit(n-1) + rabbit(n-2);
}

If you read the assignment you will see that I need to track when each 'n' enters and leaves the stack and what values are returned when they leave the stack.

I can't get the numbers 3+ to show 'Leaving Rabbit: n = 3 value = 2' etc…

I also can't figure out how to indent appropriately for the output…i know "\t" to tab but I don't know how to write something to figure out when and how many times…

my code:

int rabbit(int n) {
  cout << "Enter Rabbit: n = " << n << endl;
  if (n <= 2) {
    cout << "Leave Rabbit: n = << n << " value = 1" << endl;
    return 1;
  } else {
    return rabbit(n-1) + rabbit(n-2);
  }
}

any help will be appreciated.

It will only output the "leaving string" if (n <= 2), so what's the problem?

Here's the flow of the program:

program Rabbit;

function rabbit(n, Counter: Integer): Integer;
var
  s: string;
begin
  s := StringOfChar(' ', Counter * 2);
  WriteLn(s+'Enter Rabbit: '+IntToStr(n));
  if (n <= 2) then
  begin
    WriteLn(s+'n <= 2');
    Result := 1;
  end
  else
  begin
    WriteLn(s+'Passing though: '+IntToStr(n));
    Result := rabbit(n-1, Counter + 1) + rabbit(n-2, Counter + 1);
    WriteLn(s+'Result after passing: '+IntToStr(n));
  end;
  WriteLn(s+'Leaving Rabbit: '+IntToStr(n));
end;

begin
  rabbit(5, 0);
end.

Enter Rabbit: 5
Passing though: 5
  Enter Rabbit: 4
  Passing though: 4
    Enter Rabbit: 3
    Passing though: 3
      Enter Rabbit: 2
      n <= 2
      Leaving Rabbit: 2
      Enter Rabbit: 1
      n <= 2
      Leaving Rabbit: 1
    Result after passing: 3
    Leaving Rabbit: 3
    Enter Rabbit: 2
    n <= 2
    Leaving Rabbit: 2
  Result after passing: 4
  Leaving Rabbit: 4
  Enter Rabbit: 3
  Passing though: 3
    Enter Rabbit: 2
    n <= 2
    Leaving Rabbit: 2
    Enter Rabbit: 1
    n <= 2
    Leaving Rabbit: 1
  Result after passing: 3
  Leaving Rabbit: 3
Result after passing: 5
Leaving Rabbit: 5

In C++ though it always exits the function on a return statement. Which means that it won't ever reach either of the last 2 Writeln's which is where my problem is =p

Enter Rabbit: n = 4
   Enter Rabbit: n = 3
      Enter Rabbit: n = 2
      Leave rabbit: n = 2 value = 1
      Enter Rabbit: n = 1
      Leave rabbit: n = 1 value = 1
   Enter Rabbit: n = 2
   Leave rabbit: n = 2 value = 1

This is my output right now with this code:

#include <iostream>
using namespace std;

int rabbit(int, int);

int main() {
	int a = rabbit(4,0);
	return 0;
}

int rabbit(int n, int indent) {
	char p[] = "";
	memset(p, ' ', indent * 3);
	cout << p << "Enter Rabbit: n = " << n << endl;
	if (n <= 2) {
		cout << p << "Leave rabbit: n = " << n << " value = 1" << endl;
		return 1;
	} else {
		return rabbit(n - 1, ++indent) + rabbit(n - 2, indent++);
	}
}

I am missing the spots where it states that it is 'Leaving Rabbit: n =3,4 value = 2,3' respectively…

I don't know if there is a way to read the stack or something that I should be doing or what

That's because it also leaves in the else statement. You can just use a temporary variable to store rabbit(n - 1) + rabbit(n - 2) and then write+return it.

From: nielsie95
That's because it also leaves in the else statement. You can just use a temporary variable to store rabbit(n - 1) + rabbit(n - 2) and then write+return it.

Yea, Method opened my eyes to that. I didn't realize you could assign a recursion statement to a variable and it still work properly. Every example in class and every example in the book has the recursive statement as:

return RecFunc();

Not one example showing or stateing that you can make a variable assignment with it. I should have realized this way sooner, I was just not thinking.

I sometimes get confused and don't think clearly when programming in languages I'm not fluent in. I worry more about how I am suppose to implement it and make it work in that language rather than thinking of what I CAN do.