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assign elements to a multi-d array

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Re: assign elements to a multi-d array

#41

Mar 9th, 2007

That works! But is there a way I can ensure that the 20 locations always get filled? It seems to only get around 18

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Re: assign elements to a multi-d array

#42

Mar 9th, 2007

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Originally Posted by boujibabe

Help with Code Tags

C Syntax (Toggle Plain Text)
int countLoc(const int array2[][col], int row_size, int col_size )
{
    int count = 0;        //Stores the number of locations found
 
    for (int i=0;i<row_size;i++)
        for (int j=0;j<col_size;j++)
         if(array2[i][j] ==id)
         {
             count++;
         }
 
    return count;
}
int countLoc(const int array2[][col], int row_size, int col_size ) { int count = 0; //Stores the number of locations found for (int i=0;i<row_size;i++) for (int j=0;j<col_size;j++) if(array2[i][j] ==id) { count++; } return count; }

When you cout the locations, try the following to see if it works then:

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
for (int i=0;i<=row_size;i++) {
  for (int j=0;j<=col_size;i++) {....
for (int i=0;i<=row_size;i++) {
  for (int j=0;j<=col_size;i++) {....

This might be the reason you can only see around 18 and not an exact 20. If you sometimes, randomly, get 20 locations but never less than 18 locations, this is probably the problem.

Good luck, LamaBot

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Re: assign elements to a multi-d array

#43

Mar 10th, 2007

nope,now I'm seeing 17 and sometimes 20

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Re: assign elements to a multi-d array

#44

Mar 10th, 2007

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Originally Posted by boujibabe

nope,now I'm seeing 17 and sometimes 20

Ok, keep the code I just said to changed, changed and try this.

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
      void populate(int array[][col], int row_size, int col_size) {          
         int x, y;    
         for (int i=0;i<=row_size;i++)        
           for (int j=0;j<=col_size;j++)         
                 array[i][j] = 0;      
        srand(time(NULL)*rand());               
        for (int i=0;i<=max_total;i++) {      
           x= rand() % row_size;    
           y = rand() % col_size;      
          if(array[x][y]!=0)     
                  array[x][y] = id;         
 }/*endfor*/      
}
      void populate(int array[][col], int row_size, int col_size) {          
         int x, y;    
         for (int i=0;i<=row_size;i++)        
           for (int j=0;j<=col_size;j++)         
                 array[i][j] = 0;      
        srand(time(NULL)*rand());               
        for (int i=0;i<=max_total;i++) {      
           x= rand() % row_size;    
           y = rand() % col_size;      
          if(array[x][y]!=0)     
                  array[x][y] = id;         
 }/*endfor*/      
}

In the above code, I changed the for loops to have a "<=" that
may fixed the problem. Keep the coutLoc for loop "<=" suggestion
set along with this one, and let me know.

LamaBot.

Last edited by Lazaro Claiborn; Mar 10th, 2007 at 1:58 pm.

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Re: assign elements to a multi-d array

#45

Mar 10th, 2007

Jeez! Stop shooting in the dark and think about the problem. First, format the code properly with braces and spaces so it can be read, then:

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
void populate(int array[][col], int row_size, int col_size)
{
    int x, y;
    for (int i=0; i <= row_size; i++)  // This loop just blew your array   
                                       //    boundaries. Take it back to <
    {
        for (int j=0; j <= col_size; j++)  // Same here
        {
            array[i][j] = 0;
        }
    }            
//  srand(time(NULL) * rand());  // don't multiply by rand -- does nothing
    srand(time(NULL));
    for (int i=0; i < max_total; i++) 
    {
        do              // start a loop
        {
            x= rand() % row_size;
            y = rand() % col_size;
        } while (array[x][y] != 0); // keep looping (get new coordinates) 
                                    //   if the location is already filled
        array[x][y] = id;
    }/*endfor*/
}
void populate(int array[][col], int row_size, int col_size)
{
    int x, y;
    for (int i=0; i <= row_size; i++)  // This loop just blew your array   
                                       //    boundaries. Take it back to <
    {
        for (int j=0; j <= col_size; j++)  // Same here
        {
            array[i][j] = 0;
        }
    }            
//  srand(time(NULL) * rand());  // don't multiply by rand -- does nothing
    srand(time(NULL));
    for (int i=0; i < max_total; i++) 
    {
        do              // start a loop
        {
            x= rand() % row_size;
            y = rand() % col_size;
        } while (array[x][y] != 0); // keep looping (get new coordinates) 
                                    //   if the location is already filled
        array[x][y] = id;
    }/*endfor*/
}

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Originally Posted by LamaBot

In the above code, I changed the for loops to have a "<=" that may fixed the problem. Keep the coutLoc for loop "<=" suggestion set along with this one, and let me know.

Looping 1 extra time is not a solution for data collisions. What if you had 2 collisions before the extra loop? You'll be missing one value. What if you had no collisions before the extra loop? You'd have too many values.

The 3 Laws of the Procrastination Society:
1) Never do today that which can be put off until tomorrow
2) Tomorrow never comes

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Re: assign elements to a multi-d array

#46

Mar 10th, 2007

Problem solved by Walt's code.

LamaBot

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Re: assign elements to a multi-d array

#47

Mar 11th, 2007

Excellent! That works, thanks everyone 2d arrays are my new best friends

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Re: assign elements to a multi-d array

#48

Mar 12th, 2007

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Originally Posted by boujibabe

Excellent! That works, thanks everyone 2d arrays are my new best friends

I hope I don't "burn my bridges" by adding this but here it is. I'd like to say one thing, in reference to Walt's solution code to another. Consider the following which would do the exact same thing as Walt's for loop:

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
for (int x=0;x<max_value;x++) {
  x = rand() % row;
  y = rand() % col;
  if (array[x][y] == 0)
    array[x][y] = id;
  else
    x--;
}
for (int x=0;x<max_value;x++) {
  x = rand() % row;
  y = rand() % col;
  if (array[x][y] == 0)
    array[x][y] = id;
  else
    x--;
}

The probability of a 0 character being encountered lessens each loop. Walt's corresponding code will loop 20 * (20 - the probability factor for each successive loop) as will the above for loop, however, what makes Walt's code better is that it executes less statements when it tries to find an element that is == 0. example; say there is an array of 5 characters like this "[1][1][1][0][1]". Using Walt's code the number of statemetns executed is 3 * 4. The above for loop is 5 * 4 which is obviously more statements. This is just to emphasize on why Walt's code would be bette than the above. I add this because it is helpful to think about this too when trying to make something work.

Best regards, LamaBot

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Re: assign elements to a multi-d array

#49

Mar 12th, 2007

>Consider the following which would do the exact same thing as Walt's for loop
Are you so sure about that? You're using one of the array subscript variables 'x', as a loop index. That's certain death when you start assigning it a random value inside the loop.

"Technological progress is like an axe in the hands of a pathological criminal."

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Re: assign elements to a multi-d array

#50

Mar 12th, 2007

Well all be.... you're right Joe! Here is the oh so massive change

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
for (int i=0;i<max_value;i++) {
  x = rand() % row;
  y = rand() % col;
  if (array[x][y] == 0)
    array[x][y] = id;
  else
    i--;
}
for (int i=0;i<max_value;i++) {
  x = rand() % row;
  y = rand() % col;
  if (array[x][y] == 0)
    array[x][y] = id;
  else
    i--;
}