Multidimensional Arrays

Finally we'll take a look at multi-dimensional arrays. So far we've seen one-dimensional arrays.
int marks[10];
is a one-dimensional array. It is called one dimensional because it has only one value inside the square brackets. C++ has no limit on the number of dimensions. You can have 2 or 3 or more dimension arrays. But we shall take a look at two dimensional arrays since they will be used frequently.
Consider a two dimensional array as a tabular column with rows and columns.
int marks[3][4];
declares a two dimensional array with 3 rows and 4 columns.
COLUMNS ARE VERTICAL AND ROWS ARE HORIZONTAL.

marks[0][0]	marks[0][1]	marks[0][2]	marks[0][3]
marks[1][0]	marks[1][1]	marks[1][2]	marks[1][3]
marks[2][0]	marks[2][1]	marks[2][2]	marks[2][3]

As you can see marks[0][0] is the first square. The compiler always starts from zero and not one. Hence there are three rows and four columns in the array marks[3][4] as shown in the table above. There are a total of 12 elements.

To get the values for an array you have two ways. You have to keep asking the user statement by statement to enter a value. Or you could make use of the for loop. The best way to get the input for arrays is by making use of the for loop.

Consider the following : You want to get the values of elements of a 2 x 2 matrix (I hope you already know about matrices used in maths. If you don't then kindly email me a message : ssbell2000@yahoo.com).

int i, j, a[2][2];
for (i = 0 ; i<2 ; i ++)
{
    for (j = 0 ; j<2 ; j++)
           {
          cout<< "Enter the "<< i + 1<< " x "<< j + 1 <<"element of the matrix : ";
           cin>> a[ i ][ j ];
            }
}

I think the above code is easy to understand. For i = 0, you will have two values of j (0 and 1). Hence with this you can get the values for a[0][0] and a[0][1]. This corresponds to the first row of the matrix. For the second row, the i for loop will execute a second time with a value of 1. Hence you will get values for a[1][0] and a[1][1].

In the cout statement I have mentioned i + 1 and j + 1. This is just for the display. Remember that the compiler will start numbering from zero. The first element for the compiler will be the 0 x 0 element. For the user it is better if you refer to the first element as 1 x 1.

You'll understand the usefulness of two dimensional arrays in the Projects Section 3