5.5 Multidimensional Arrays

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Arrays can have more than one dimension. The declaration for a two-dimensional array is:

   type     variable   [   size1   ][   size2   ]; // comment 

For example:

 // a typical matrix int matrix[2][4]; 

Notice that C++ does not follow the notation used in other languages of matrix[10,12] .

To access an element of the matrix we use the following notation:

 matrix[1][2] = 10; 

C++ allows you to use as many dimensions as needed (limited only by the amount of memory available). Additional dimensions can be tacked on:

 four_dimensions[10][12][9][5]; 

Initializing multidimensional arrays is similar to initializing single-dimension arrays. A set of curly braces { } encloses each element. The declaration:

 // a typical matrix int matrix[2][4]; 

can be thought of as a declaration of an array of dimension 2 whose elements are arrays of dimension 4. This array is initialized as follows :

 // a typical matrix int matrix[2][4] =      {          {1, 2, 3, 4},          {10, 20, 30, 40}      }; 

This is shorthand for:

 matrix[0][0] = 1; matrix[0][1] = 2; matrix[0][2] = 3; matrix[0][3] = 4; matrix[1][0] = 10; matrix[1][1] = 20; matrix[1][2] = 30; matrix[1][3] = 40; 

Question 5-2: Why does the program in Example 5-9 print incorrect answers?

Example 5-9. array/array.cpp

 #include <iostream> int array[3][5] = {     // Two dimensional array    { 0,  1,  2,  3,  4 },    {10, 11, 12, 13, 14 },    {20, 21, 22, 23, 24 } }; int main(  ) {     std::cout << "Last element is " << array[2,4] << '\n';     return (0); } 

When run on a Sun 3/50 this program generates:

 Last element is 0x201e8 

Your answers may vary.

You should be able to spot the error because one of the statements looks like it has a syntax error in it. It doesn't, however, and the program compiles because we are using a new operator that has not yet been introduced. But even though you don't know about this operator, you should be able to spot something funny in this program.

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