1 Dimensional hollow grid array?

[Kingassassinable]

Hi there. I've been tasked with creating a simple console game with some tasks included on how to complete it. My first task is to
"
1. Write code which asks the user which size environment they want to play in and read user input of width and height.
2. Use these values to create a 1-dimentional array of size width * height.
3. Clear the array by setting all elements to ‘ ‘ (space).
4. Edge the array with ‘*’ symbols. Populate the array with a random scattering of ‘*’. See
screengrab above.

The "screengrab" for clarification looks like this:
https://gyazo.com/09f52ba8e7316d1bb2e5bead238ab7b2

Okay so I'm on the step of trying to create this hollow grid with a border of '*'s and I have code for it but I think something must be wrong with it. I'm not great with this, as when I've had a similar task before, we weren't using arrays to make the grid. Any help would be greatly appreciated!

  std::cout << "To set the environment, please enter the width and the height:" << std::endl;
	std::cout << "Width: ";
	std::cin >> width;
	std::cout << "Height: ";
	std::cin >> height;
	std::cout << std::endl;

	gridArray = new char[width * height];

	for (int i = 0; i < width * height; i++)
	{
		gridArray[i] = ' ';
	}

	for (int j = 0; j < width; j++)
	{
		gridArray[j] = '*';
		gridArray[(width * height) - j] = '*';
	}

	for (int k = 0; k < height; k++)
	{
		gridArray[(k * width)] = '*';
		gridArray[(k * width) - 1] = '*';
	}

[jonnin]

to map 2d into 1d in a C array, the formula is
[desired_row*maxcols+desired_col]
that is the same as a 2-d array
grid[desired_row][desired_col];

Is that what you are trying to do / asking?

[Kingassassinable]

Yeah, trying to represent a 1d array as a multidimensional as stated in the tasks. I need to have it have the border around the edge and then will have to have random obstacles inside the grid too.

[jonnin]

ok... so you should be able to populate the "matrix" using that formula.
you can memset the top and bottom to * if you want, fast and 1 line of code.
Then you can loop over the rest, * out the sides (maxcol-1 and 0th col) and randomize the others?

I don't see exactly what is wrong with what you have, but that should work.
Easier, initialize all to * and randomize the middle part..

[AbstractionAnon]

//  Convert a 2 dim row and col to a 1 dim index
int index (int r, int c, int w)
{  return r * w + c;
}

void make_top_border (char grid[], int w, int h)
{   int r = 0;
    for (int c=0; c<w; c++)
        grid[index(r,c,w)] = '*';
}
        
void make_bottom_border (char grid[], int w, int h)
{   int r = h-1;

    for (int c=0; c<w; c++)
        grid[index(r,c,w)] = '*';
}
        
void make_left_border (char grid[], int w, int h)
{   int c = 0;

    for (int r=0; r<h; r++)
        grid[index(r,c,w)] = '*';
}

void make_right_border (char grid[], int w, int h)
{   int c = w-1;

    for (int r=0; r<h; r++)
        grid[index(r,c,w)] = '*';
}

[jonnin]

yes, that looks right to me, I think you are getting it.

I would still just do
memset(grid, '*', width*height); //I think, double check... memeset must be used with care.
and then do

int r,c;
for(r = 1; r < height -1; r++)
for(c = 1; c < width-1; c++)
{
double d = rand();
if (rand < -0.1) //10% chance
grid[index(r,c,w)] = '*'; //hopefully I didnt revers r and c there... trying to multi-task here
else
grid[index(r,c,w)] = ' ';
}

and call it good. But I prefer less lines of code generally.

[Kingassassinable]

Can I just say, going back to the original post, I am doing all of this in a class member function. Therefore I can't be declaring new local functions inside. Can someone please just explain what I have to change from my original code for it to work the way I want? I feel like there's just a simple change to perform.

[jonnin]

std::cout << "To set the environment, please enter the width and the height:" << std::endl;
	std::cout << "Width: ";
	std::cin >> width;
	std::cout << "Height: ";
	std::cin >> height;
	std::cout << std::endl;

	gridArray = new char[width * height];
       memset (gridArray, '*',  width*height); //again, test this by itself, stop here and run it.  
                                                                  //should print the grid as all *s
                             //it is possible I have the parameters to memset out of order..!!!

        srand((int)clock());  //or whatever seed. might use a constant seed until debugged. 

      int r,c;
      for(r = 1; r < height-1; r++)
      for(c = 1; c< width-1; c++)
        if(rand() > 0.1) 
          gridArray[r*width+c] = ' '; //90% are turned to spaces.  the others are already *s. 

//done!

you need <cmemory> for memset. You need something for rand, I think its in <cstdlib>, I forget. I don't use it much and forget. Its possible to unroll that loop into a single for loop, but I can't think thru that right this min.

[Kingassassinable]

I need to be able to make this without the use of memset as we haven't been taught that and I don't believe they would be happy with it. What is a simple solution to changing my current code to make it work? As I believe it is a simple change, but don't know what.

[jonnin]

memset replaces

for(i = 0; i < width*height; i++)
gridArray[i] = '*';

with one faster, smaller, better line of code. You can use the loop if you fear to get ahead of your class. Most teachers seem to like it when a student learns stuff outside of class, though. You could use it to brown - nose :)

[Kingassassinable]

Alright, thanks mate

[jonnin]

Anytime. I am about to go offline... if you have any trouble, let me know right away. Ive done a lot of 1-d matrix math, but trying to help you while in a meeting at work, which has my concentration a bit muddled.