Initializing 2d array with variables

[jeffsg605]

How do I declare this array?

char array[rows][cols];

The user needs to be able to specify the number of rows and columns. I'm not having much luck searching around.

Thanks

[soultrip]

you're going to have problems using an array for that since an array's memory is allocated at compile time. you'll never be able to allow a user to dynamically allocate the size of an array unless you use some type of dynamic structure like a linked list or a flex array or something similar

[Zhuge]

You can dynamically allocate the size of an array with new. You'll need to use a loop to do the higher dimensions, though.

[jeffsg605]

How would I go about that?

[marklycris05]

remember the goto x,y jeff..

x is going to the right or left, while the y is going up or down.


x<------------------>x


y
/\
l
l
l
l
l
\/
y


x,y

x is the cols, and y is the rows.


try ask for the user how many cols and store it to a variable called cols, then create another one ask for rows and store it to a variable called rows. you can have your array[cols][rows]..

[ausairman]

If I want to create a 2d array with variable column/row size I usually do it like this:

char * myarray;

int main () {
    // do something to get my row and column values here

    myarray = new char [row*col];

    // now let's say I want to access row 5, column 6 (0 being the first, not 1);

    char row_5_col_6 = myarray[row*5+6];
    return 0;
}

I don't know if this is conventional or not, but it does work...

[jeffsg605]

Well this will compile but not run;

int main()
{
	int cols = 10;
	int rows = 10;
	char **myArray;
	 myArray = new char*[rows];
	 myArray[rows] = new char[cols];

	 for( int i = 0; i < rows; i++ )
	 {
		 for ( int j = 0; j < cols; j++ )
		 {
			 myArray[i][j] = 'X';
		 }
	 }
	 for( int i = 0; i < rows; i++ )
	 {
		 for ( int j = 0; j < cols; j++ )
		 {
			 cout << myArray[i][j];
		 }
	 }
}

It does that thing where it says the program has stopped working.

[shacktar]

myArray = new char*[rows];
myArray[rows] = new char[cols];

First thing wrong with this is there are 10 rows (so indexes 0 through 9) and the second line is indexing 10, which is an array out of bounds.

What you need to do is initialize each row (myArray[0] through myArray[9]) with new. So, each row is a char array of size cols. You need to initialize this in a loop. Remember you need a matching delete [] when you're done with the arrays for each call to new[].

[jeffsg605]

Ha! I love this forum. Thanks shacktar.