Programming Forums > Application Development > C

Fall Back Son · Mar 25th, 2007, 11:30 AM

I'm using two dimensional arrays to simulate an ocean which contains an oil spill. The wind pushes the oil, and it moves in the ocean (aka array). So I have to make calculations (where the wind pushes the oil) on the values of my "original" ocean and those become the values in the "new" ocean. However, whenever I try this, I print out the new array every x time units. I am getting huge answers that are incorrect. I'll post my code shortly. . thanks for any help (no code though, please).

Fall Back Son · Mar 25th, 2007, 11:48 AM

Ok, no longer getting huge answers that don't make sense.. but smaller answers that don't make sense, and my ocean isn't spreading enough.

Btw, the reason for all the if statements is that the array can't be evaluated at -1 or anything greater than "SIZE" .

Fall Back Son · Mar 25th, 2007, 11:55 AM

(Toggle Plain Text)

/* this function should "blow" the oil to the West in this manner:
the start space ends up with half it's original oil. the two spaces directly above and below the start space get 5% of the start space's oil. The space up and to the right of the start space gets 10% . the space down and right gets 10%. The space to the right of the start space gets 20% */


void West (int OldOceanArray[SIZE][SIZE], int TransitionOcean[SIZE][SIZE])
{

   int i ;
   int j ;

   for (i = 0; i < SIZE; i++)
   {
      for (j = 0; j < SIZE; j ++)
      {

TransitionOcean[i][j] = (OldOceanArray[i][j]/2) + OldOceanArray[i][j];

         if (i != SIZE)
         {

TransitionOcean[i+1][j] = (OldOceanArray[i][j] * (.05)) + OldOceanArray[i+1][j];
         }

         if (i != 0)
         {
TransitionOcean[i-1][j] = (OldOceanArray[i][j] * (.05)) + OldOceanArray[i-1][j];
         }

         if (i != 0 && j != SIZE)
         {
TransitionOcean[i-1][j+1] = (OldOceanArray[i][j] * (.1)) + OldOceanArray[i-1][j+1];
         }

         if (j != SIZE)
         {
TransitionOcean[i][j+1] = (OldOceanArray[i][j] * (.2)) + OldOceanArray[i][j+1];
         }

         if (i != SIZE && j != SIZE)
         {
TransitionOcean[i+1][j+1] = (OldOceanArray[i][j] * (.1)) + OldOceanArray[i+1][j+1];
         }



      }
   }

   for (i = 0; i < SIZE; i ++)
   {
      for (j = 0; j < SIZE; j++)
      {
         OldOceanArray[i][j] = TransitionOcean[i][j];
      }
   }
}

*bummed*

Fall Back Son · Mar 25th, 2007, 2:21 PM

please... help me

The Dark · Mar 25th, 2007, 5:51 PM

(Toggle Plain Text)

         if (i != SIZE)

In the array, you are allowed to access coordinates from 0 to SIZE-1, your test allows your code to access coordinates of SIZE (i.e. when i is SIZE-1). This means you are accessing values outside of your oceans boundaries.
Try changing the test (and all the other SIZE tests) to

(Toggle Plain Text)

         if (i != SIZE - 1)

Fall Back Son · Mar 25th, 2007, 6:03 PM

thanks, tried it already though. that's also why I thought my answers were incorrect.

Fall Back Son · Mar 25th, 2007, 6:04 PM

New code:

/* This code is different because it relies on the fact that each "square" of the array should receive a certain percent of the oil from the squares around it. */

(Toggle Plain Text)

void West (int OldOceanArray[SIZE][SIZE], int TransitionOcean[SIZE][SIZE])
{

   int i ;
   int j ;


   for (i = 0; i < SIZE; i++)
   {
      for (j = 0; j < SIZE; j ++)
      {
         TransitionOcean[i][j] = (OldOceanArray[i][j]/2) + (OldOceanArray[i+1][j]/20) + (OldOceanArray[i-1][j]/20) + (OldOceanArray[i][j-1]/5) + (OldOceanAr\
ray[i+1][j-1]/10) + (OldOceanArray[i-1][j-1]/10);

      }
   }

   for ( i = 0 ; i < SIZE ; i ++)
   {
      for (j = 0 ; j < SIZE ; j ++)
      {
   OldOceanArray[i][j] = TransitionOcean[i][j];
      }
   }

Fall Back Son · Mar 25th, 2007, 6:13 PM

I don't know what I'm doing wrong (obviously) but I continue to get negative answers.

I'm going to put the if statements back in for this. that should eliminate the negative answers, but they will still be wrongl ol.

Duck · Mar 25th, 2007, 6:28 PM

(In your last code snippet)..You'll also be accessing memory outside the arrays boundaries when i or j equals zero, since:

OldOceanArray[i-1][j-1]

Fall Back Son · Mar 25th, 2007, 6:28 PM

No. My answers are still negative. I don't understand how I can be getting negative answers, considering there is a check in place (with what you said, SIZE - 1) for both i and j. I'm trying to make the program go through the for loop, and for each square of the temporary "ocean" (TransitionOcean) fill it with the appropriate values from the OldOceanArray. Each square should get 50% of what it used to have, 5% from the square above it, 5% from the square below it, 20% from the square behind it, and ten percent from both the square down and left & the square down and right. If I use the for loop to do these calculations for each square, and do it for every square, shouldn't I get the right answers?

Despite the various ways I've tried the math, nothing has gotten correct answers. And this method as well as several other methods I have used make sense from a mathematical standpoint, I believe, so it must be something I am doing in the program which is wrong.

Mar 25th, 2007, 11:30 AM	#1
Fall Back Son Hobbyist Programmer Join Date: Oct 2006 Posts: 204 Rep Power: 2	Question about two dimensional arrays. I'm using two dimensional arrays to simulate an ocean which contains an oil spill. The wind pushes the oil, and it moves in the ocean (aka array). So I have to make calculations (where the wind pushes the oil) on the values of my "original" ocean and those become the values in the "new" ocean. However, whenever I try this, I print out the new array every x time units. I am getting huge answers that are incorrect. I'll post my code shortly. . thanks for any help (no code though, please).

Mar 25th, 2007, 11:55 AM	#3
Fall Back Son Hobbyist Programmer Join Date: Oct 2006 Posts: 204 Rep Power: 2	(Toggle Plain Text) /* this function should "blow" the oil to the West in this manner: the start space ends up with half it's original oil. the two spaces directly above and below the start space get 5% of the start space's oil. The space up and to the right of the start space gets 10% . the space down and right gets 10%. The space to the right of the start space gets 20% / void West (int OldOceanArray[SIZE][SIZE], int TransitionOcean[SIZE][SIZE]) { int i ; int j ; for (i = 0; i < SIZE; i++) { for (j = 0; j < SIZE; j ++) { TransitionOcean[i][j] = (OldOceanArray[i][j]/2) + OldOceanArray[i][j]; if (i != SIZE) { TransitionOcean[i+1][j] = (OldOceanArray[i][j] (.05)) + OldOceanArray[i+1][j]; } if (i != 0) { TransitionOcean[i-1][j] = (OldOceanArray[i][j] * (.05)) + OldOceanArray[i-1][j]; } if (i != 0 && j != SIZE) { TransitionOcean[i-1][j+1] = (OldOceanArray[i][j] * (.1)) + OldOceanArray[i-1][j+1]; } if (j != SIZE) { TransitionOcean[i][j+1] = (OldOceanArray[i][j] * (.2)) + OldOceanArray[i][j+1]; } if (i != SIZE && j != SIZE) { TransitionOcean[i+1][j+1] = (OldOceanArray[i][j] * (.1)) + OldOceanArray[i+1][j+1]; } } } for (i = 0; i < SIZE; i ++) { for (j = 0; j < SIZE; j++) { OldOceanArray[i][j] = TransitionOcean[i][j]; } } } /* this function should "blow" the oil to the West in this manner: the start space ends up with half it's original oil. the two spaces directly above and below the start space get 5% of the start space's oil. The space up and to the right of the start space gets 10% . the space down and right gets 10%. The space to the right of the start space gets 20% / void West (int OldOceanArray[SIZE][SIZE], int TransitionOcean[SIZE][SIZE]) { int i ; int j ; for (i = 0; i < SIZE; i++) { for (j = 0; j < SIZE; j ++) { TransitionOcean[i][j] = (OldOceanArray[i][j]/2) + OldOceanArray[i][j]; if (i != SIZE) { TransitionOcean[i+1][j] = (OldOceanArray[i][j] (.05)) + OldOceanArray[i+1][j]; } if (i != 0) { TransitionOcean[i-1][j] = (OldOceanArray[i][j] * (.05)) + OldOceanArray[i-1][j]; } if (i != 0 && j != SIZE) { TransitionOcean[i-1][j+1] = (OldOceanArray[i][j] * (.1)) + OldOceanArray[i-1][j+1]; } if (j != SIZE) { TransitionOcean[i][j+1] = (OldOceanArray[i][j] * (.2)) + OldOceanArray[i][j+1]; } if (i != SIZE && j != SIZE) { TransitionOcean[i+1][j+1] = (OldOceanArray[i][j] * (.1)) + OldOceanArray[i+1][j+1]; } } } for (i = 0; i < SIZE; i ++) { for (j = 0; j < SIZE; j++) { OldOceanArray[i][j] = TransitionOcean[i][j]; } } } bummed

Mar 25th, 2007, 5:51 PM	#5
The Dark Expert Programmer Join Date: Jun 2005 Posts: 825 Rep Power: 4	(Toggle Plain Text) if (i != SIZE) if (i != SIZE) In the array, you are allowed to access coordinates from 0 to SIZE-1, your test allows your code to access coordinates of SIZE (i.e. when i is SIZE-1). This means you are accessing values outside of your oceans boundaries. Try changing the test (and all the other SIZE tests) to (Toggle Plain Text) if (i != SIZE - 1) if (i != SIZE - 1)

Mar 25th, 2007, 6:04 PM	#7
Fall Back Son Hobbyist Programmer Join Date: Oct 2006 Posts: 204 Rep Power: 2	New code: /* This code is different because it relies on the fact that each "square" of the array should receive a certain percent of the oil from the squares around it. */ (Toggle Plain Text) void West (int OldOceanArray[SIZE][SIZE], int TransitionOcean[SIZE][SIZE]) { int i ; int j ; for (i = 0; i < SIZE; i++) { for (j = 0; j < SIZE; j ++) { TransitionOcean[i][j] = (OldOceanArray[i][j]/2) + (OldOceanArray[i+1][j]/20) + (OldOceanArray[i-1][j]/20) + (OldOceanArray[i][j-1]/5) + (OldOceanAr\ ray[i+1][j-1]/10) + (OldOceanArray[i-1][j-1]/10); } } for ( i = 0 ; i < SIZE ; i ++) { for (j = 0 ; j < SIZE ; j ++) { OldOceanArray[i][j] = TransitionOcean[i][j]; } } void West (int OldOceanArray[SIZE][SIZE], int TransitionOcean[SIZE][SIZE]) { int i ; int j ; for (i = 0; i < SIZE; i++) { for (j = 0; j < SIZE; j ++) { TransitionOcean[i][j] = (OldOceanArray[i][j]/2) + (OldOceanArray[i+1][j]/20) + (OldOceanArray[i-1][j]/20) + (OldOceanArray[i][j-1]/5) + (OldOceanAr\ ray[i+1][j-1]/10) + (OldOceanArray[i-1][j-1]/10); } } for ( i = 0 ; i < SIZE ; i ++) { for (j = 0 ; j < SIZE ; j ++) { OldOceanArray[i][j] = TransitionOcean[i][j]; } }

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Mar 25th, 2007, 11:48 AM	#2
Fall Back Son Hobbyist Programmer Join Date: Oct 2006 Posts: 204 Rep Power: 2	Ok, no longer getting huge answers that don't make sense.. but smaller answers that don't make sense, and my ocean isn't spreading enough. Btw, the reason for all the if statements is that the array can't be evaluated at -1 or anything greater than "SIZE" .

Mar 25th, 2007, 2:21 PM	#4
Fall Back Son Hobbyist Programmer Join Date: Oct 2006 Posts: 204 Rep Power: 2	please... help me

Mar 25th, 2007, 6:03 PM	#6
Fall Back Son Hobbyist Programmer Join Date: Oct 2006 Posts: 204 Rep Power: 2	thanks, tried it already though. that's also why I thought my answers were incorrect.

Mar 25th, 2007, 6:13 PM	#8
Fall Back Son Hobbyist Programmer Join Date: Oct 2006 Posts: 204 Rep Power: 2	I don't know what I'm doing wrong (obviously) but I continue to get negative answers. I'm going to put the if statements back in for this. that should eliminate the negative answers, but they will still be wrongl ol.

Mar 25th, 2007, 6:28 PM	#9
Duck Programmer Join Date: Jun 2006 Location: England London Posts: 72 Rep Power: 3	(In your last code snippet)..You'll also be accessing memory outside the arrays boundaries when i or j equals zero, since: OldOceanArray[i-1][j-1]

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Programming Forums > Application Development > C

Question about two dimensional arrays.