Initialize a 2D Java Array with different values on each side

Question

I am learning to work with 2D arrays and was tasked with creating a 5x5 game board with different values on the side with the middle row having two pieces on each side of an empty space totaling twelve pieces each.

However I can't figure out the logic to switch characters in the middle

        grid = new char[ROWS][COLS];
    //initialize to starting configuration
    char frogs = 'F';
    for (int i = 0; i < ROWS; i++){
        for (int j = 0; j < COLS; j++){
            grid[i][j] = frogs;
        }
    }
    char toads = 'T';
    for (int i = ROWS -3; i < ROWS; i++){
        for (int j = 0; j < COLS; j++){
            grid[i][j] = toads;
        }
    }
    grid[ROWS - 3][COLS - 3] = EMPTY_SPACE;

Welcome to SO. Please specify the expected Output and where your code is failing to help us help you. — Exception_al
– Exception_al, Commented Feb 20, 2018 at 14:41
The expected output would be a 5x5 table with the first two rows the char of F and the last two rows a char of T. The middle row should start with two chars of F followed by an empty space and then by two more T characters. I believe my code fails after I set the toads variable because it just resets the middle row to all T's. — Michael
– Michael, Commented Feb 20, 2018 at 14:47
Please format your code to make it readable. Please try to privde a stackoverflow.com/help/mcve . Please update your question with what the requirements more clearly. — Exception_al
– Exception_al, Commented Feb 20, 2018 at 14:48

Exception_al · Accepted Answer · 2018-02-20 15:14:53Z

Here,

for (int i = 0; i < ROWS; i++){
        for (int j = 0; j < COLS; j++){
            grid[i][j] = frogs;
        }
    }

you set all the rows to frogs whereas you wish to fill only the first 2 (or first half rows with frogs

In the second set of nested for loop,

char toads = 'T';
    for (int i = ROWS -3; i < ROWS; i++){
        for (int j = 0; j < COLS; j++){
            grid[i][j] = toads;
        }
    }

you set the last 3 rows to toads whereas you wish only to fill the last 2 rows with toads.

You are filling the Array even though you wish it differently.

A possible solution (close to your code for easy understanding) to this could be the below. Notice also the comments inline, and please also note that this could be done differently as well :

char[][] grid = new char[ROWS][COLS];
// initilize only the first 2 (5/2 = 2 integer) rows with frogs
char frogs = 'F';
for (int i = 0; i < COLS; i++) {
    for (int j = 0; j < ROWS/2; j++) {
        grid[j][i] = frogs;
    }
}
char toads = 'T';
// fill the last 2 (starting from the last one (ROWS-1) and decreasing to ROWS/W (5/2 = 2) with toads
for (int i = ROWS - 1; i > ROWS/2; i--) {
    for (int j = 0; j < COLS; j++) {
        grid[i][j] = toads;
    }
}

// fill the middle row 
for(int j=0;j<COLS;j++) {
    if(j<COLS/2)
        grid[COLS/2][j]=frogs;
    else if(j>COLS/2)
        grid[COLS/2][j]=toads;
    else
        grid[COLS/2][j]=' ';
}

A simplified and short solution could be (kindly go through ternary operator, which is like a shorthand if-then-else, in Java Documentation to understand how this works ) :

for (int i = 0; i < ROWS; i++) {
            for (int j = 0; j < COLS; j++) {
                grid[i][j] = i < ROWS / 2 ? frogs : i > ROWS / 2 ? toads : j < COLS / 2 ? frogs : j > COLS / 2 ? toads : ' ';
            }
        }

All the above considering that you also intend to change the ROWS and COLS to other values, otherwise I like Code-Apprentice's idea to initialize it statically and avoid the hassle altogether.

Code-Apprentice · Accepted Answer · 2018-02-20 15:08:40Z

0

Since you only want the first two rows to be frogs, you should only iterate over the first two rows rather than over all of them:

char frogs = 'F';
for (int i = 0; i < 2; i++){
    for (int j = 0; j < COLS; j++){
        grid[i][j] = frogs;
    }
}

Note how i < ROWS changed to i < 2. You can treat the last two rows similarly.

Note that since this is a small array, it makes sense to just hard code the initial values:

char grid[i][j] = {
                    {'F', 'F', 'F', 'F', 'F'},
                    {'F', 'F', 'F', 'F', 'F'},
                    {'F', 'F', ' ', 'T', 'T'},
                    {'T', 'T', 'T', 'T', 'T'},
                    {'T', 'T', 'T', 'T', 'T'},
                  }

answered Feb 20, 2018 at 15:08

Code-Apprentice

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MAV · Accepted Answer · 2018-02-20 17:59:23Z

0

for (int i = 0; i < COLS; i++)
{
     for (int j = 0; j < ROWS; j++)
     {
       if(j < 2)
       {
          grid[i][j] = frogs;
       }
       else if(j > 2)
       {
         grid[i][j] = toads;
       }
       else
       {
          if(i < 2)
          {
              grid[i][j] = frogs;
          }
          else if(i > 2)
          {
              grid[i][j] = toads;
          }
          else
          {
              grid[i][j] = ' ';
          }
       }
     }
}

edited Feb 20, 2018 at 17:59

answered Feb 20, 2018 at 15:00

MAV

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