Program to move box in a jar - what is wrong?

**Fredir** · 12-07-2007

I am writing this program to move a box in a jar(a larger array). First, I overlap the box into the array, then I print the array and attempt to move it. But for some reason, the moving part of the code only works when the box is set entirely to true and not for the set up I have now. Can anyone see what I am doing wrong? - the code compiles, so this should help visualizing what the code is about.

Code:

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;
#define MAX_HEIGHT 20
#define MAX_WIDTH 10
#define MAX_SIZE 4

void main()
{
	int k =0;
	int l =0;
	int firstRow = 0; //these will come as parameters
	int firstCol = 3;


//------------------------For testing-------------------//
	bool jar[MAX_HEIGHT][MAX_WIDTH];
	for(int i = 0; i < MAX_HEIGHT; i++)
	{
		for(int j = 0; j < MAX_WIDTH; j++)
		{
			jar[i][j] = false;
		}
	} 

	bool box[MAX_SIZE][MAX_SIZE];

	for(int i = 0; i < MAX_SIZE; i++)
		for(int j = 0; j < MAX_SIZE; j++)
	{
		box[i][j] = false;

	} 
		box[1][2] = true;
		box[1][3] = true;
		box[2][1] = true;
		box[2][2] = true;

	//print box
	for(int row =0; row < MAX_SIZE; row++)
	{
		for (int col = 0; col < MAX_SIZE; col ++)
			cout << box[row][col];
		cout << endl;
	}
//-------------------------------------------------------------//
		for(k = 0; k < MAX_SIZE; k++) //assigns the box to that location of the jar
			for(l = 0; l < MAX_SIZE; l++)
				for(int n = firstRow; n < firstRow + 4; n++)
					for(int m = firstCol; m < firstCol + 4; m++)
					{
						if(jar [k][l+3] == false && box [k][l] == true)
						{jar [k][l+3] = true;
						}
						if(jar [k][l+3] == true && box [k][l] == false)
						{jar [k][l+3] = false;
						}
						
					}
//prints the original array for testing


	for (int i = 0; i < MAX_HEIGHT; i++)
		{
			for(int j = 0; j < MAX_WIDTH; j++) 
			{
				if(jar[i][j] == true)
				{
					cout << "H";
				}
				else
				{
					cout << ".";
				}
			}
			cout << endl;
		}

//Main function: After key is input, move array on jar.
	char direction;
	cin >> direction;

	if(direction == 's')
	{
		for(int y = firstRow; y < firstRow + 4; y++)
			for(int x = firstCol; x < firstCol + 4; x++)
			{
				jar[y+1][x] = jar[y][x];
			}
			for(int z = firstCol; z < firstCol + 4; z++)
				jar[firstRow][z] = false;
	}

	else if(direction == 'd')
	{
		for(int y = firstRow; y < firstRow + 4; y++)
			for(int x = firstCol; x < firstCol + 4; x++)
			{
				jar[y][x+1] = jar[y][x];
			}
			for(int z = firstRow; z < firstRow + 4; z++)
				jar[z][firstCol] = false;

	}
	else if(direction == 'a')
	{
		for(int y = firstRow; y < firstRow + 4; y++)
			for(int x = firstCol; x < firstCol + 4; x++)
			{
				jar[y][x-1] = jar[y][x];
			}
			for(int z = firstRow; z < firstRow + 4; z++)
				jar[z][firstCol + 3] = false;
		
	}

//---------------Prints array again for testing----------------------//
	for (int i = 0; i < MAX_HEIGHT; i++)
		{
			for(int j = 0; j < MAX_WIDTH; j++) 
			{
				if(jar[i][j] == true)
				{
					cout << "H";
				}
				else
				{
					cout << ".";
				}
			}
			cout << endl;
		}


}

Thank you.

**vart** · 12-07-2007

assigns the box to that location of the jar

in this place you have 4 loop while using only 2

jar[y+1][x] = jar[y][x];

y+1 is overwritten, so on the next iteration of the loop it has not the value you expect. move box starting from the right column - not left

and move down starting with the last row, not the first.

Maybe start with the simple example - try to write memmove that works for overlaping regeons to see when you start copy from the first char and when - from the last. You will need to use the same principle

**Fredir** · 12-07-2007

What you mean four loops, the last two are to delete the line on the top.

I really don't see how starting from the bottom would matter. Can someone suggest a correction?

**ZuK** · 12-07-2007

Originally Posted by Fredir

What you mean four loops, the last two are to delete the line on the top.

I really don't see how starting from the bottom would matter. Can someone suggest a correction?

Yeah, when moving to the left or up start copy from lowest to highest index.
When moving right or down copy from highest to lowest index.
But that has been said before.
Kurt

**Fredir** · 12-07-2007

can anyone explain why that makes a difference?

**tabstop** · 12-07-2007

Well, let's look at it then:

Code:

if(direction == 's')
	{
		for(int y = firstRow; y < firstRow + 4; y++)
			for(int x = firstCol; x < firstCol + 4; x++)
			{
				jar[y+1][x] = jar[y][x];
			}
			for(int z = firstCol; z < firstCol + 4; z++)
				jar[firstRow][z] = false;
	}

I realize everything here is boolean, but let's look at integers. Suppose jar[y][x] = y, so jar[1][x] = 1, jar[4][x] = 4, and so on; and let's also suppose that firstRow = 1. What happens?

y goes from 1 through 4; in each of our columns we first set jar[2][x] to jar[1][x], so jar[2][x] is now 1. Then we set jar[3][x] to jar[2][x], so jar[3][x] is now 1 (remember that we just changed jar[2][x]!); then jar[4][x] to jar[3][x] = 1, and jar[5][x] to jar[4][x] = 1.

So instead of moving four rows down one each, we moved one row down four times. This is why, when we are moving data, we must loop against the direction of the move; otherwise, we will overwrite data that hasn't gotten moved yet.

**anon** · 12-07-2007

Imagine you have an array with values {1, 2, 3, 4, 0}. Now suppose you wanted to move the first four values right. If you go copy values left to right then after the first iteration you'll have {1, 1, 3, 4, 0}, after second {1, 1, 1, 4, 0} and finally {1, 1, 1, 1, 1}. If you iterated from end to beginning then the iterations would result in:
{1, 2, 3, 4, 4}
{1, 2, 3, 3, 4}
{1, 2, 2, 3, 4}
{1, 1, 2, 3, 4}
and you'll have to do something about the first element.

**iMalc** · 12-07-2007

Originally Posted by Fredir

can anyone explain why that makes a difference?

this is the simplest possible example that demonstrates why:
Imagine you have a 1D array with 3 items;

Code:

int x[3] = {10, 20, 30};

Now, you want to move the first two items over by one place, dropping whatever value was previously in the last spot, and filling the first spot with zero. i.e. it should end up with this:
(0, 10, 20)
This seems so simple that we don't even need a loop, we can simply unroll the loop in our head and would come up with this:

Code:

x[1] = x[0];
x[2] = x[1];
x[0] = 0;

Okay, now try executing that:

Code:

x[1] = x[0];
// The array now holds (10, 10, 30)
x[2] = x[1];
// The array now holds (10, 10, 10)
x[0] = 0;
// The array now holds (0, 10, 10)

Oh no!!!

Now you write the backwards copying case.

**Fredir** · 12-07-2007

Thank you for the help everyone--I decremented the indexes on the down and right shift. Here is the updated code:

Code:

// Practice 2.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;
#define MAX_HEIGHT 20
#define MAX_WIDTH 10
#define MAX_SIZE 4

void main()
{
	int k =0;
	int l =0;
	int firstRow = 0; //these will come as parameters
	int firstCol = 3;


//------------------------For testing-------------------//
	bool jar[MAX_HEIGHT][MAX_WIDTH];
	for(int i = 0; i < MAX_HEIGHT; i++)
	{
		for(int j = 0; j < MAX_WIDTH; j++)
		{
			jar[i][j] = false;
		}
	} 
		


	bool box[MAX_SIZE][MAX_SIZE];

	for(int i = 0; i < MAX_SIZE; i++)
		for(int j = 0; j < MAX_SIZE; j++)
	{
		box[i][j] = false;

	} 
		box[1][2] = true;
		box[1][3] = true;
		box[2][1] = true;
		box[2][2] = true;

	//print box
	for(int row =0; row < MAX_SIZE; row++)
	{
		for (int col = 0; col < MAX_SIZE; col ++)
			cout << box[row][col];
		cout << endl;
	}
//-------------------------------------------------------------//
		for(k = 0; k < MAX_SIZE; k++) //assigns the box to that location of the jar
			for(l = 0; l < MAX_SIZE; l++)
				for(int n = firstRow; n < firstRow + 4; n++)
					for(int m = firstCol; m < firstCol + 4; m++)
					{
						if(jar [k][l+3] == false && box [k][l] == true)
						{jar [k][l+3] = true;
						}
						if(jar [k][l+3] == true && box [k][l] == false)
						{jar [k][l+3] = true;
						}
						
					}
//prints the original array for testing


	for (int i = 0; i < MAX_HEIGHT; i++)
		{
			for(int j = 0; j < MAX_WIDTH; j++) 
			{
				if(jar[i][j] == true)
				{
					cout << "H";
				}
				else
				{
					cout << ".";
				}
			}
			cout << endl;
		}

//Main function: After key is input, move array on jar.
	char direction;
	cin >> direction;

	if(direction == 's')
	{
		for(int y = firstRow + 3; y>=0; y--)
			for(int x = firstCol; x < firstCol + 4; x++)
			{
				jar[y+1][x] = jar[y][x];
			}
			for(int z = firstCol; z < firstCol + 4; z++)
				jar[firstRow][z] = false;
			//score++;
	}

	else if(direction == 'd')
	{
		for(int y = firstRow; y < firstRow + 4; y++)
			for(int x = firstCol + 3; x >=0; x--)
			{
				jar[y][x+1] = jar[y][x];
			}
			for(int z = firstRow; z < firstRow + 4; z++)
				jar[z][firstCol] = false;

	}
	else if(direction == 'a')
	{
		for(int y = firstRow; y < firstRow + 4; y++)
			for(int x = firstCol; x < firstCol + 4; x++)
			{
				jar[y][x-1] = jar[y][x];
			}
			for(int z = firstRow; z < firstRow + 4; z++)
				jar[z][firstCol + 3] = false;
		
	}

//---------------Prints array again for testing----------------------//
	for (int i = 0; i < MAX_HEIGHT; i++)
		{
			for(int j = 0; j < MAX_WIDTH; j++) 
			{
				if(jar[i][j] == true)
				{
					cout << "H";
				}
				else
				{
					cout << ".";
				}
			}
			cout << endl;
		}


}

--> Does anyone see anything wrong with it? (Especially with that 4 nested for loops to overlap the box and jar.) I admit I just guesses at some point and the loop stated working.

Thanks.

**Fredir** · 12-07-2007

Also, I added an new if thing for rotation but it doesn't seem to be working. I am kind of losing my mind over this right now. If anyone can shed some light on this statement as well, I would highly appreciate it.

Code:

else if (direction == 'w')
	{
		for(int i=0; i<4; i++)
			for(int j=0; j<4; j++)
				box[3-j][ i ]=box[ i ][j];

			for(int row =0; row < MAX_SIZE; row++)
	{
		for (int col = 0; col < MAX_SIZE; col ++)
			cout << box[row][col];
		cout << endl;
	}

	}

**vart** · 12-08-2007

you still have 4 loop while using 2:

Code:

		for(k = 0; k < MAX_SIZE; k++) //assigns the box to that location of the jar
			for(l = 0; l < MAX_SIZE; l++)
				for(int n = firstRow; n < firstRow + 4; n++)
					for(int m = firstCol; m < firstCol + 4; m++)
					{
						if(jar [k][l+3] == false && box [k][l] == true)
						{jar [k][l+3] = true;
						}
						if(jar [k][l+3] == true && box [k][l] == false)
						{jar [k][l+3] = true;
						}
						
					}

And do not tell me you are deleting something here. m and n are not used.

**Fredir** · 12-08-2007

Ok, but regarding my last post about the rotation part, why is it not displaying anything at all on the jar array?

**anon** · 12-08-2007

Is this going to be a tetris-like game? I recently wrote one (code can be found in the game downloads) and I found it to be easier to manipulate the moving block as an array of coordinate-pairs in its own small bounding box and updating its relative position and checking collisions against the tetris field.

**Fredir** · 12-08-2007

Yes, I am doing something similar.

**Fredir** · 12-08-2007

Can anyone spot anything wrong with the 'w' (rotation) part???

Thank you so much.

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