TK1914: C++ Programming

Array II

FTSM :: TK1914, 20112012 2

Objective

In this chapter you will explore how to manipulate data in a two-dimensional array.

FTSM :: TK1914, 20112012 3

Two-Dimensional Arrays

• A collection of a fixed number of components arranged in two dimensions– All components are of the same type

• Declaration syntax:

dataType arrayName[intexp1][intexp2];

where intexp1 and intexp2 are expressions yielding positive integer values, which specify number of rows and number of columns respectively

• Sometimes called matrices or tables

FTSM :: TK1914, 20112012 4

mark

[0]

[1]

[2]

[3]

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

• Example:

int mark[4][5];

FTSM :: TK1914, 20112012 5

Initialization

• Like one-dimensional arrays– Two-dimensional arrays can be initialized when they

are declared

• Example:– int mark [][] = { {87, 86, 88, 82, 89},

{64, 69, 60, 63, 66},{91, 90, 94, 98, 93},{77, 74, 75, 72, 70} };

mark

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

[0] [1] [2] [3] [4]88 89828687

94 9398909175 70727477

60 66636964

inner braces can be omitted

FTSM :: TK1914, 20112012

Accessing Array Components

• The syntax to access a component of a two-dimensional array is:

arrayName[indexexp1][indexexp2]where indexexp1 and indexexp2 are expressions yielding nonnegative integer values

• indexexp1 specifies the row position and indexexp2 specifies the column position

6

FTSM :: TK1914, 20112012 7

Accessing Array Components

• Example:temp = mark[2][4]

• Example: find sum of elements in second row.row = 1;sumRow = 0;for (int col = 0; col < 5; col++)

sumRow = sumRow + mark[row][col];

mark

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

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

88 89828687

94 9398909175 70727477

60 66636964

FTSM :: TK1914, 20112012

Processing Two-Dimensional Arrays

• A two-dimensional array can be processed in three different ways:

1. Process the entire array

2. Process a particular row of the array, called row processing

3. Process a particular column of the array, called column processing

8

FTSM :: TK1914, 20112012

Processing Two-Dimensional Arrays (continued)

• Each row and each column of a two-dimensional array is a one-dimensional array

• When processing a particular row or column of a two-dimensional array

– we use algorithms similar to processing one-dimensional arrays

9

FTSM :: TK1914, 20112012 10

prog09.9.cpp

FTSM :: TK1914, 20112012 11

FTSM :: TK1914, 20112012 12

FTSM :: TK1914, 20112012 13

FTSM :: TK1914, 20112012 14

Passing Two-Dimensional Arrays as Parameters to Functions

• Two-dimensional arrays can be passed as parameters to a function

• By default, arrays are passed by reference• The base address, which is the address of the first

component of the actual parameter, is passed to the formal parameter

• When declaring a two-dimensional array as a formal parameter– can omit size of first dimension, but not the second

• Number of columns must be specified

FTSM :: TK1914, 20112012 15

#include <iostream> #include <iomanip>

using namespace std;

const int NUMBER_OF_ROWS = 6;const int NUMBER_OF_COLUMNS = 5;

void printMatrix(int matrix[][NUMBER_OF_COLUMNS], int NUMBER_OF_ROWS);void sumRows(int matrix[][NUMBER_OF_COLUMNS], int NUMBER_OF_ROWS);void largestInRows(int matrix[][NUMBER_OF_COLUMNS], int NUMBER_OF_ROWS);

Example 9-10 (pg 528)

prog09.10.cpp

FTSM :: TK1914, 20112012 16

int main() { int board[NUMBER_OF_ROWS][NUMBER_OF_COLUMNS] = {{23, 5, 6, 15, 18}, {4, 16, 24, 67, 10}, {12, 54, 23, 76, 11}, {1, 12, 34, 22, 8}, {81, 54, 32, 67, 33}, {12, 34, 76, 78, 9}}; //Line 1

printMatrix(board, NUMBER_OF_ROWS); //Line 2 cout << endl; //Line 3 sumRows(board, NUMBER_OF_ROWS); //Line 4 cout << endl; //Line 5 largestInRows(board, NUMBER_OF_ROWS); //Line 6}

FTSM :: TK1914, 20112012 17

Example: Matrix manipulation#include <iostream>using namespace std;const int N = 3;

void inputMatrix(int mat[][N], int n);void addMatrix(int mat1[][N], int mat2[][N], int mat3[][N],

int n);void outputMatrix(int mat[][N], int n);

void main() {int matrix1[N][N], matrix2[N][N], output[N][N];cout << "Input matrix 1: " << endl;inputMatrix(matrix1, N);cout << "Input matrix 2: " << endl;inputMatrix(matrix2, N);addMatrix(matrix1, matrix2, output, N);cout << "Answer for matrix1 add matrix2: " << endl;outputMatrix(output, N);

}

FTSM :: TK1914, 20112012 18

void inputMatrix(int mat[][N], int size) {int i, j;for (i = 0; i < size; i++)

for (j = 0; j < size; j++) cin >> mat[i][j];

}

void addMatrix(int mat1[][N], int mat2[][N], int mat3[][N], int size) {int i, j;for (i = 0; i < size; i++)

for (j = 0; j < size; j++) mat3[i][j] = mat1[i][j] + mat2[i]

[j];}

void outputMatrix(int mat[][N], int size) {int i, j;for (i = 0; i < size; i++) {

for (j = 0; j < size; j++) cout << mat[i][j];

cout << endl;}

}

FTSM :: TK1914, 20112012 19

Exercise

• Write matrix manipulation functions as listed below:– substract two matrices– multiply two matrices– to calculate transpose of a matrix

• Write function calls in the main program to test your matrix manipulation functions

FTSM :: TK1914, 20112012

Summary

• In a two-dimensional array, the elements are arranged in a table form

• To access an element of a two-dimensional array, you need a pair of indices: one for the row position and one for the column position

• In row processing, a two-dimensional array is processed one row at a time

• In column processing, a two-dimensional array is processed one column at a time

20

FTSM :: TK1914, 20112012

Summary (continued)

• In row processing, a two-dimensional array is processed one row at a time

• In column processing, a two-dimensional array is processed one column at a time

21