Multi Dimensional Arrays

• Page 548 through the end of the chapter.
• We have been dealing with one dimensional arrays.
• But we can add higher dimensions.
  • Think chess board.
  • Or even a rubix cube
  • Or a change in space (3d) over time (4d).
• Careful, these can grow very large very fast.
• type identifier [const int expression][const int expression] ...
• In two dimensions
  • The first dimension is usually considered the rows
  • The second is considered the columns.

• const size_t ROWS=5;
  const size_t COLS = 3;
  ...
  char board[ROWS][COLS];
  

  	0	1	2
  0	board[0][0]	board[0][1]	board[0][2]
  1	board[1][0]	board[1][1]	board[1][2]
  2	board[2][0]	board[2][1]	board[2][2]
  3	board[3][0]	board[3][1]	board[3][2]
  4	board[4][0]	board[4][1]	board[4][2]

• We could initialize the entire thing to be 0.

• size_t i,j;
  
  for(i=0; i<ROWS; i++) {
     for(j=0; j<COLS; j++) {
        board[i][j] = 0;
     }
  }
  

• Passing multi dimensional arrays
  • You must provide the sizes of all but the first dimension when passing as parameters.

  • void PrintBoard(int theBoard[][COLS]);
    

  • But at this point, it is probably better to use all dimensions

  • void PrintBoard(int theBoard[ROWS][COLS]);
    

• The typedef command.
  • This command allows the program to nickname an existing data type.
  • typedef known_type identifier;
  • For example, this MIGHT in a header file somewhere
  • typedef unsigned long size_t;
  • This just means that anywhere the compiler sees size_t, it replaces it with unsigned long.
• So this is common

  const int ROWS=5;
  const int COLS=3;
  
  typedef int BoardArrayT[ROWS][COLS];
  
  void PrintBoard(BoardArrayT board);
      

• Sometimes it is easier to think a little different.
• I have a class of up to 40 names.

• const size_t MAX_STUDENTS = 40;
  
  typedef string ClassT[MAX_STUDENTS];
      

• Then I can declare a set of classes

• const size_t MAX_CLASES;
  
  ClassT classes[MAX_CLASSES];
  size_t classSizes[MAX_CLASSES];