Introduction to Two-Dimensional Arrays

Two-dimensional arrays, the most common multidimensional arrays, are used to store information that we normally represent in table form. Two-dimensional arrays, like one-dimensional arrays, are homogeneous. This means that all of the data in a two-dimensional array is of the same type. Examples of applications involving two-dimensional arrays include:

• a seating plan for a room (organized by rows and columns),
• a monthly budget (organized by category and month), and
• a grade book where rows might correspond to individual students and columns to student scores.

Declaration of Two-Dimensional Arrays

Example: The following declarations set aside storage for a two-dimensional array called labScores which contains 40 rows and 14 columns. Rows correspond to a particular student and columns correspond to a particular lab score.

        const int JAN_WAN = 10;

        const int SOURCECODEERA_WAN = 20;

        int SOURCECODE [JAN_WAN][ SOURCECODEERA_WAN];

Example: A sample of a 2-D array initialize to 0

#include<iostream>   //Allow program to preform input/output operation

using namespace std; //Allow to group entities like class

int main()

{

            //Declaration of 2D array variable

    int arr[8][12] = {0}; //Initialize array to 0. Creates a 8*12 matrix or a 2d array

            //A nested for loop is use to go through the element within the array

            for(int r = 0; r < 8; r++) //(The Row) This loop  will go one time while

            {

                        for(int c = 0; c < 12; c++) //(The Column) This loop will go 12 times

                        {

                                    cout<<arr[r][c];   //Display the element within the array

                        }

                        cout<<endl;    //New line

            }

            system("pause");

            return 0;

}

Exercise 1:
Show C++ statements to declare the following two-dimensional array:

Declare a two-dimensional array which can be used to store a yearly budget. Each row of the array corresponds to a particular budgeted item like rent, electric, etc. There are at most 15 items to be budgeted. Each column of the array corresponds to a month, January, February, etc. Of course there are 12 columns corresponding to the 12 months of the year. All the data to be placed in the array consists of real numbers.

Manipulation of a two-dimensional array requires the manipulation of two indices. When the two-dimensional array labScores is declared, enough storage is set aside to hold a table containing 40 rows and 14 columns for a total of 40 * 14 = 560 integer values. To access one particular value, we must specify the row and column. The row index ranges from 0 to MAX_STUDENTS-1 (39) and the column index ranges from 0 to MAX_LABS-1 (13). Thus the table can be visualized as:

This two-dimensional array may also be visualized as a one-dimensional array of arrays. An alternative view of this array would be:

This two-dimensional array may be viewed as a one-dimensional array having 40 elements where each element is an array of 14 values.

Accessing a Two-Dimensional Array Element
In our labScores example, suppose we wish to indicate that the second student (corresponding to row 1) made a 90 on lab 10 (corresponding to column 9). We might use the statement:

labScores [1][9] = 90;

Array indices may be integer constants (as in the above example), variables, or expressions. They should be within the bounds of the array.

  Two-Dimensional Array Initialization
We can declare and initialize an array A as follows:

        //declaration

        int A[3][4] = {{8, 2, 6, 5},     //row 0

                     {6, 3, 1 ,0},      //row 1

                     {8, 7, 9, 6}};     //row 2

Memory for the array may be visualized as:

J.W. Production