How to do this

[lr_potti]

Dear All,

I am new to C/C++. I have written a small program for copying
2 different 2D array into a single 3D array in a most stupid
way. Certainly there will be diiferent ways to solve it.

I need to reduce no of lines of the program.

Please suggest how to do this


//program for copying
2 different 2D array into a single 3D array

#include <string.h>
#include <stdio.h>

int *a; // 3D array
int *b; // 1st 2D array
int *c; // second array

void main()
{

a = new int[2*3*3];
b = new int[3*3];
c = new int[3*3];
int i,j,k;

//memset((void*)c,0,3*3*sizeof(int));
//memset((void*)b,1,3*3*sizeof(int));

// INitializing two arrays
for(i=0;i<3;i++)
for(j=0;j<3;j++)
{
c[i*3+j] = 2;
//printf("%d\n",c[i*3+j]);
}
for(i=0;i<3;i++)
for(j=0;j<3;j++)
{
b[i*3+j] = 1;
//printf("%d\n",b[i*3+j]);
}
//memcpy((void*)b,(void*)c,3*3*sizeof(int));


//copying the first 2D array into 3D array
for(i=0;i<1;i++)
for(j=0;j<3;j++)
for(k=0;k<3;k++)
{
a[k*3+j*3+i] = c[i*3+j];
printf("%d\n",/*c[i*3+j],*/a[k*3+j*3+i]);
}

//copying the second 2D array into the 3D array

for(i=1;i<2;i++)
for(j=0;j<3;j++)
for(k=0;k<3;k++)
{

a[k*3+j*3+i] = b[i*3+j];
printf("%d\n",/*c[i*3+j],*/a[k*3+j*3+i]);
}

//Displaying the 3D array
for(i=0;i<2;i++)
for(j=0;j<3;j++)
for(k=0;k<3;k++)
{
//printf("%d\n",a[k*3+j*3+i]);
}
}


Thanks in advance
RAMACHANDRAN LAKSMI NARAYAN

[namezero111111]

Why not memcpy the arrays? As long as their data types are POD, there's not problem. Otherwise you should use std::copy.

Have you made any progress on this so far?
Note that nested loops can get very slow at level 3 and up, so you should avoid that - especially if the inner loop were to be more complicated.


-Andy

[lr_potti]

Dear sir,

Thanks a lot. Memcpy is not working in my case.
How to rewrite the code using memcpy.

Thanks in advance

[dcjr84]

1) Use [ code ][ /code ] tags when posting source code.

2) Your header files are incorrect. Standard library headers with .h are not used anymore.
(Though I see you use printf(), so this is probably some old C code which allows them)
Should be...

#include <cstring>
#include <cstdio>

3) Also, don't forget to use the standard namespace when you change the header files

using namespace std;

4) main() return an int type, not void. Using void is incorrect.

int main()

[exterminator]

You code does not work. Have you tested it? The indexing is totally flawed. This is a working version with a little changes. Try using functions further to it:

#include <iostream>
using namespace std;
int main()
{
	int *a; // 3D array
	int *b; // 1st 2D array
	int *c; // second array

	a = new int[2*3*3];
	b = new int[3*3];
	c = new int[3*3];
	int i,j,k;

	// INitializing two arrays
	for(i=0;i<3;i++)
	{
		for(j=0;j<3;j++)
		{
			c[i*3+j] = i*3+j+2;
			cout << c[i*3+j] << "\t";
		} 
		cout << "\n";
	}
	cout << "\n";
	for(i=0;i<3;i++)
	{
		for(j=0;j<3;j++)
		{
			b[i*3+j] = i*3+j+1;
			cout << b[i*3+j] << "\t";
		}
		cout << "\n";
	}
	cout << "\n";

	//copying the first 2D array into 3D array
	i=0;
	for(j=0;j<3;j++)
	{
		for(k=0;k<3;k++)
		{
			a[i*9+j*3+k] = c[j*3+k];
		}
	}

	//copying the second 2D array into the 3D array
	i=1;
	for(j=0;j<3;j++)
	{
		for(k=0;k<3;k++)
		{
			a[i*9+j*3+k] = b[j*3+k];
		}
	}

	//Displaying the 3D array
	for(i=0;i<2;i++)
	{
		for(j=0;j<3;j++)
		{
			for(k=0;k<3;k++)
			{
				cout << a[i*9+j*3+k] << "\t";
			}
			cout << "\n";
		}
		//cout << "\n";
	}
	cout << "\n";
	return 0;
}

The copy code (shown in italics above) can be reduced to just this much:

	std::copy(c, c+9, a);
	std::copy(b, b+9, a+9);

You would need to include <algorithm>

Lastly, the arrays you have are one dimensional, not 2-dimensional or 3-dimensional as you're thinking. However, that can be interpreted as a 2-d array at most. The third one "a" is a 2-d array only which is what would have been a result of merge between "b" and "c".

Take a look at the how to encapsulate a 2-d array and work with them. You can add a member function merge() to it in order to achieve the functionality you tried getting here. Here's the link:

• How to declare and use two-dimensional arrays?