Need Help With Arrays!!!

Psychomachy · #1 03-Feb-2009, 12:11

Okay, this is my second semester in a C++ class, so I'm still new at this, and we're on multidimensional arrays.

Here's the problem:

The array is 120 by 120, and I need to put values in each one of those spots, of which are two numbers, I'll call them x and y.

Another factor is the 120 by 120 are divided into columns and rows, I'll call them i and j.

The array will look something like this:

x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
y y y x x x y y y x x x y y y
y y y x x x y y y x x x y y y
y y y x x x y y y x x x y y y
y y y x x x y y y x x x y y y
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x

..... so like a checkerboard...
120 of these across, in this case, 120/40 = i across
and 120/30 = j
x x x
x x x
x x x
x x x

I hoooopppeee all this makes sense

, sorry....(please help!)

The problem I am having is inserting the x's and the y's into the array, and how they go in the correct location, I also do not know the numbers that i and j represent.

fakepoo · #2 03-Feb-2009, 13:22

You could create nested loops:

CPP / C++ / C Code:

int i, j;
char board[120][120];

for(i=0;i<120;++i)
{
  for(j=0;j<120;++j)
  {
    if( (i%6 <  3 && j%6 <  3) || 
        (i%6 >= 3 && j%6 >= 3) 
      ) board[i][j] = 'x';
    else board[i][j] = 'y';
  }
}

Psychomachy · #3 03-Feb-2009, 13:31

Quote:

Originally Posted by fakepoo

You could create nested loops:

CPP / C++ / C Code:

int i, j;
char board[120][120];

for(i=0;i<120;++i)
{
  for(j=0;j<120;++j)
  {
    if( (i%6 <  3 && j%6 <  3) || 
        (i%6 >= 3 && j%6 >= 3) 
      ) board[i][j] = 'x';
    else board[i][j] = 'y';
  }
}

why the 6s and 3s?

Psychomachy · #4 03-Feb-2009, 14:04

I implemented that code into my program, and the output was a bit different than I needed, maybe a mistake, it was like this

xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy
xxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxx
xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy

rather than:

xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy
yyyxxxyyyxxxyyyxxx
yyyxxxyyyxxxyyyxxx
yyyxxxyyyxxxyyyxxx
xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy
xxxyyyxxxyyyxxxyyy

fakepoo · #5 03-Feb-2009, 14:11

Based on your pattern...

Code:

x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
y y y x x x y y y x x x y y y
y y y x x x y y y x x x y y y
y y y x x x y y y x x x y y y
y y y x x x y y y x x x y y y
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x
x x x y y y x x x y y y x x x

...you need to check to see which column and row an 'x' would exist. When we take the row and divide by 6, we need to know what the remainder is and that is our offset from position 0. We know that offsets of 0, 1, or 2 will be the first group and 3, 4, or 5 will be the second group.

Code:

x x x y y y x x x y y y x x x

Notice that the bolded 'x' in the above row has an index of 7. It's offset would then be 7%6 which is 1. Because 1 is less than 3, it goes in the first group. This group could be an 'x' or a 'y' depending on the group from the column.

Does this make sense?

fakepoo · #6 03-Feb-2009, 14:17

CPP / C++ / C Code:

#include <iostream>
using namespace std;

#define ROWS 20
#define COLS 20

int main()
{
	int i, j;
	char board[ROWS][COLS];

	for(i=0;i<ROWS;++i)
	{
	  for(j=0;j<COLS;++j)
	  {
		if( (i%6 <  3 && j%6 <  3) || 
			(i%6 >= 3 && j%6 >= 3) 
		  ) board[i][j] = 'x';
		else board[i][j] = 'y';
	  }
	}

	// Print the board
	for(i=0;i<ROWS;++i)
	{
	  cout << endl;
	  for(j=0;j<COLS;++j)
	  {
		cout << board[i][j];
	  }
	}
	
	getchar();
	return 0;
}

I used this exact code and it worked exactly as expected.

Psychomachy · #7 03-Feb-2009, 14:48

Thank you, I think I understand now

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