Problem with recursive function

This is a discussion on Problem with recursive function within the C Programming forums, part of the General Programming Boards category; Hello, I am writing a program that navigates a maze. I am trying to use a recursive function to do ...

  1. #1
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    Oct 2009
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    Problem with recursive function

    Hello,

    I am writing a program that navigates a maze. I am trying to use a recursive function to do so. My problem is the function stops working partway through. This is the maze I am using:

    ooooooooooo
    o ```````` o
    o`ooooooo `o
    o+o```````o
    ooo`ooooooo
    o$o``````$o
    o`o`ooooooo
    o````````-o
    ooooooooooo

    The function gets as far as this and quits

    ooooooooooo
    o ########o
    o #ooooooo `o
    o+o```````o
    ooo`ooooooo
    o$o``````$o
    o`o`ooooooo
    o````````-o
    ooooooooooo



    Code:
    void findDollar ( maz_t  *t){ // function to find checkpoint
    
    	int i, j;
    
    	 for (i=0;i<row;i++){  // loop to find a checkpoint
    		for(j=0;j<column;j++){
    			if (t->map[i][j] == '$'){
    				t->dollarX = i;
    				t->dollarY = j;
    			}
    		}
    	 }
    	
    
    	if(t->map[t->startx-1][t->starty] != 'o' && t->map[t->startx-1][t->starty] != '#'){ // moves up
    		  t->map[t->startx-1][t->starty] = '#';
    		  t->startx = t->startx-1;
    		
    	}
    	    else if(t->map[t->startx+1][t->starty] != 'o' && t->map[t->startx+1][t->starty] != '#'){ // moves down
    		  t->map[t->startx+1][t->starty] = '#';
    		  t->startx = t->startx+1;
    		}
    	      else if(t->map[t->startx][t->starty-1] != 'o' && t->map[t->startx][t->starty-1] != '#'){ // moves to the left
    		  t->map[t->startx][t->starty-1] = '#';
    		  t->starty = t->starty-1;
    		  }
    		  
    	        else if(t->map[t->startx][t->starty+1] != 'o' && t->map[t->startx][t->starty+1] != '#'){ // moves to the right
    		    t->map[t->startx][t->starty+1] = '#';
    		    t->starty = t->starty+1;
    			}
    		
    			if (t->startx != t->dollarX && t->starty != t->dollarY){  // If the checkpoint has not been reached, call function again.
    			findDollar(t);
    			}
    
    
      }// end function
    I'm assuming that it's something with the way I am directing it to move down, but I can't see the problem. Any help would be greatly appreciated.

  2. #2
    spurious conceit MK27's Avatar
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    I haven't totally dissected this but based on what you say don't you think the problem will be here:

    Code:
     if (t->startx != t->dollarX && t->starty != t->dollarY){  // If the checkpoint has not been reached, call function again.
    			findDollar(t);
    			}
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  3. #3
    Registered User
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    Oct 2009
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    Sorry, I don't understand.

    I also tried using
    Code:
    	while (t->startx != t->dollarX && t->starty != t->dollarY){ 
    			findDollar(t);
    			}
    and

    Code:
    			while (t->map[t->dollarX][t->dollarY] != '#'){  
    			findDollar(t);
    			}
    Ive gotten the same results with both. Anything else I tried gives me a stack overflow.

  4. #4
    Super Moderator VirtualAce's Avatar
    Join Date
    Aug 2001
    Posts
    9,598
    You can do this much easier with a stack.

    1. Pick a starting point
    2. Push current location on the stack
    3. Pick a random direction
    4. If open, move there and goto 2
    5. If not open, pop off the stack and goto 3
    6. Repeat until all cells have been checked.

  5. #5
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    Unfortunately for me, this assignment is due in an hour and a half. I think I'm stuck with trying to figure out this method.

  6. #6
    Registered User
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    From the code it's not obvious what's going on, so post the algorithm you're using to navigate this maze.

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