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Recursion problem

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Recursion problem

 
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  #1
Jul 6th, 2009
Hey i m reading tutrial about rucursion and got code whish isnt complicated or anything but i dunno why it prints the way it does
C Syntax (Toggle Plain Text) 
  1. /* recur.c -- recursion illustration */
  2.  
  3. #include <stdio.h>
  4.  
  5. void up_and_down(int);
  6.  
  7.  
  8.  
  9. int main(void)
  10.  
  11. {
  12.  
  13.     up_and_down(1);
  14.  
  15.     return 0;
  16.  
  17. }
  18.  
  19.  
  20.  
  21. void up_and_down(int n)
  22.  
  23. {
  24.  
  25.     printf("Level %d: n location %p\n", n, &n); /* 1 */
  26.  
  27.     if (n < 4)
  28.  
  29.          up_and_down(n+1);
  30.  
  31.     printf("LEVEL %d: n location %p\n", n, &n); /* 2 */
  32.  
  33.  
  34.  
  35. }
here it prints
Level 1: n location 0022FF60
Level 2: n location 0022FF40
Level 3: n location 0022FF20
Level 4: n location 0022FF00
LEVEL 4: n location 0022FF00
LEVEL 3: n location 0022FF20
LEVEL 2: n location 0022FF40
LEVEL 1: n location 0022FF60


first i know why it prints from 1 to 3 but see here it keeps calling itself till number is smaller than 4 right then after it finishes it goes back to that printf after that if statement whish should print the normal i whish is 1 but it doesnt it prints 4 4 3 2 1 why it got decremented there nowhere in the code where it said i-1 even when the function called itself even if we alrdy specified i as 1 and function calling itself somehow decremented it should when i==3 that if statement will terminate whish will print then orginal i ?
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Re: Recursion problem

 
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  #2
Jul 6th, 2009
At the tip, you've got
C Syntax (Toggle Plain Text) 
  1. up_and_down(1)
  2.   up_and_down(2)
  3.     up_and_down(3)
  4.       up_and_down(4)
There is no subtraction, just a nested set of values stored as local parameter 'n'.
As you return from each recursive call, you get back the previous value of n.
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Re: Recursion problem

 
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  #3
Jul 6th, 2009
oh so it keep calling function till ruc level 4 then it goes to other function whish level 3 then level 2 then level 1 again whish is the main one ?
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Re: Recursion problem

 
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  #4
Jul 6th, 2009
Exactly.
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Re: Recursion problem

 
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  #5
Jul 6th, 2009
oh thanks if only the book would put it in that simple
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Re: Recursion problem

 
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  #6
Jul 6th, 2009
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Originally Posted by MrNoob View Post
Hey i m reading tutrial about rucursion and got code whish isnt complicated or anything but i dunno why it prints the way it does
C Syntax (Toggle Plain Text) 
  1. /* recur.c -- recursion illustration */
  2.  
  3. #include <stdio.h>
  4.  
  5. void up_and_down(int);
  6.  
  7.  
  8.  
  9. int main(void)
  10.  
  11. {
  12.  
  13.     up_and_down(1);
  14.  
  15.     return 0;
  16.  
  17. }
  18.  
  19.  
  20.  
  21. void up_and_down(int n)
  22.  
  23. {
  24.  
  25.     printf("Level %d: n location %p\n", n, &n); /* 1 */
  26.  
  27.     if (n < 4)
  28.  
  29.          up_and_down(n+1);
  30.  
  31.     printf("LEVEL %d: n location %p\n", n, &n); /* 2 */
  32.  
  33.  
  34.  
  35. }
here it prints
Level 1: n location 0022FF60
Level 2: n location 0022FF40
Level 3: n location 0022FF20
Level 4: n location 0022FF00
LEVEL 4: n location 0022FF00
LEVEL 3: n location 0022FF20
LEVEL 2: n location 0022FF40
LEVEL 1: n location 0022FF60


first i know why it prints from 1 to 3 but see here it keeps calling itself till number is smaller than 4 right then after it finishes it goes back to that printf after that if statement whish should print the normal i whish is 1 but it doesnt it prints 4 4 3 2 1 why it got decremented there nowhere in the code where it said i-1 even when the function called itself even if we alrdy specified i as 1 and function calling itself somehow decremented it should when i==3 that if statement will terminate whish will print then orginal i ?
[B]reply:as the last printf stement s the part of the function up n down it will be executed as many times as the function is called,but before the statement is executed the function is called again and again untill n becomes4. now when the func is excuted for the last time it executes the last printf statement and returns to its calling function to execute it's last printf statement.hence the pattern 4 3 2 1.
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