Multidimensional arrays

Section 8.7  Multidimensional arrays

Two-dimensional array

A structure for storing multiple values of the same type 
organized by rows and columns:

int exam_scores[100][4];

This might be a collection of exam scores for a class of 100 
students who took 4 exams.

Scores for 4th student would be stored as:

exam_scores[3][0], exam_scores[3][1], exam_scores[3][2], 
exam_scores[3][3]



For a tic-tac-toe game, there is a board of 9 squares (3 rows 
and 3 columns) and each square contains a character:’X’, 
‘O’, or ‘ ‘  (blank).

char tic_tac_toe[3][3];

Or use the following to declare and initialize the array to all 
blanks:

char tic_tac_toe[3][3] = { {‘ ‘, ‘ ‘, ‘ ‘}, {‘ ‘, ‘ ‘, ‘ ‘}, 
  {‘ ‘, ‘ ‘,‘ ‘}};

or

char tic_tac_toe[3][3] = { {‘X‘, ‘ ‘, ‘X‘}, {‘O‘, ‘O‘, ‘ ‘}, 
  {‘X‘, ‘ ‘,‘O‘}};

X |   |X 
O |O|  
X |   |O

Last element is tic_tac_toe[2][2] and its contents is ‘O’.

How is tic_tac_toe actually stored in memory – memory is 
not “rectangular”, but is linear.

Address   contents

1000 tic_tac_toe[0][0]
1001   	tic_tac_toe[0][1]         first row
1002   	tic_tac_toe[0][2]
1003   	tic_tac_toe[1][0]
1004   	tic_tac_toe[1][1]
…
1008  	tic_tac_toe[2][2]        last element in last row

Function diagonal-win . Returns 1 (true) if there is a winner 
in a diagonal for a specified player and 0 (false) if there is 
no diagonal winner.

int diagonal_winner (char tic_tac_toe[][3], char player)
{
   /* Return true if all 3 diagonal squares contain player */
    if ((tic_tac_toe[0][0] == player) && (tic_tac_toe[1][1] 
          == player) && (tic_tac_toe[2][2] == player)) ||
          …

         return 1;
    else
         return 0;
}

int diagonal_winner (char tic_tac_toe[][3], char player)
{
   /* Return true if all 3 diagonal squares contain player */
    return ((tic_tac_toe[0][0] == player) && 
                (tic_tac_toe[1][1] == player) && 
                (tic_tac_toe[2][2] == player)  ||
                …

}

Let’s look at what is stored in tic_tac_toe in function data 
area:

tic_tac_toe
1000 (address of tic_tac_toe[0][0])

From the formal argument declaration char 
tic_tac_toe[0][3], C compiler “knows” that there are 3 
elements in each row, so when it has to access 
tic_tac_toe[1][1], it accesses the fifth element in the array 
that starts at address 1000 (3 elements in row 0, 
tic_tac_toe[1][0] and then tic_tac_toe[1][1] in 2nd row).

Function get_move – to read and store the move of a 
human opponent (player):

void get_move (tic_tac_toe[][3], char player)
{
    int row, col;

do
{     printf(“Enter row & then column of next move:”);
       row = get_integer(1, 3);
       col = get_integer(1, 3);
       row--;
       col--;
      /* check for empty square. */
      if (tic_tac_toe[row][col] != ‘ ‘)
            printf(“Square if filled – try again”);
} while (tic_tac_toe[row][col] != ‘ ‘);

       /* Human chose an empty square – fill it. */
        tic_tac_toe[row][col] = player;
}

Write a move function for the computer. Computer moves 
to first empty square it finds. Begins looking in row 0, then 
row 1, then row 2. Store machine character in first empty 
square you find and then execute return statement (without 
a value).

void make_move(tic_tac_toe[][3], char machine)
{
     for (          )
         for (         )
             if (         )
            {
                   tictactoe[    ][    ] = machine;
                   printf(“Machine moves to square in row %d”,
				row,
				“, column %d\n”, col);
                   return;
            }
}

Think about what the main function might look like for a 
tic-tac-toe game player – computer plays ‘X’ and human 
plays ‘O’.

#define human ‘O’
#define computer ‘X’

Read in next player (‘X’ or ‘O’)
do
{
    if next player is human {
         read human’s move
        next player is machine
    } else {
         compute machine’s move
         next player is human
    }

     display(tic_tac_toe);   
 } while game is not over

if winner is player ‘X’
    display message that computer wins
else if winner is player ‘O’
    display message that human wins
else
    display that game is a draw

Back to the exam score array.

int score[100][3];

Write a function that returns the average score on all 3 
exams for a particular student indicated by the function 
argument stu_index.

Write a function that returns the average score for all 
students (argument num_students indicates how many 
students there are) on a particular exam (argument 
exam_index).