COMPUTER PROGRAMMING (TMK 3102) LECTURE NOTES 9

8/9/2019 COMPUTER PROGRAMMING (TMK 3102) LECTURE NOTES 9

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9. Array

Knowledge:

Understand the execute technique of array

Skill:Can write application program using one and two dimensionalarray


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TMK3102 PENGATURCARAAN KOMPUTER JUL 2006/20072

Why Array?

Assume that you were asked to write aprogram that accept 10 student marks,

calculating average mark, and then print out

number of students that get more thanaverage mark.

How to store all these marks?

Consider the following..(recall)


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public class Average {

public static void main(String[] args) {

//variables declaration

int mark1,mark2,mark3,mark4,mark5;

int mark6,mark7,mark8,mark9,mark10;

int studentNumbers, totalMark;

float markAverage;

Scanner input = new Scanner(System.in);

Variables Declaration

Solution Without Array (1/6)


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//get student mark

System.out.print(Mark 1:);mark1 = input.nextInt();

System.out.print(Mark 2:);

mark2 = input.nextInt();





Get Inputs



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//get student mark








What would happen if there were 1000 students?



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//calculate total marks

totalMarks = mark1 + mark2 + mark3 + mark4+ mark5 + mark6 + mark7 + mark8 + mark9+ mark10;

//calculate average mark

markAverage = totalMark/10;




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//calculate number of student above average

if (mark1 > markAverage) studentNumber++;if (mark2 > markAverage) studentNumber++;

if (mark3 > markAverage) studentNumber++;










//print the result

System.out.println(number of student thatget more than average = +

studentNumber);}

}




Instead of using 10 variables to represent 10 student

marks,another technique is using one-dimensional

array for storing a list of marks.

Array is a collection of memory location that is used

for storing data with the same type. Each memorylocation in array is referred by arrays name and

location memory index.

Array (Definitions)



Normal Variable

int mark;

Array Variable

int[] mark = new int[10];

mark

mark[1]mark[2]

mark[3]

mark[4]

mark[5]mark[6]

mark[7]

mark[8]

mark[9]

mark[0]

Array VS NormalVariables

mark



67

mark

34

76

47

82

54

38

72

63

24

[0]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

Single element in array

is retrieved using index

Indices start from 0;the 1st element of an

array mark is referred toas mark[0] and the n-thelement as mark[n-1].

An index can have anyint value from 0 toarrays length - 1.

Indices (Subscript)(1/2)

A

r

ra

y

In

d

e

x



67

34

76

47

82

54

38

72

63

24

[0]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

An index is written within squarebrackets after arrays name

To retrieve 1st element in array

To retrieve 6th element in array.

To retrieve nthelement in array

element1=mark[0];

Array Index

Indices (Subscript)(2/2)

element6=mark[5];

Array Index

elementn=mark[n-1];

mark



Syntax 1

DataType [ ] variableName = new DataType[arraysize

of type integer]

Example :define an array variable called monthName oftype String with length 12

String[ ] monthName = new String[12];

Declare One Dimensional Array (1/3)



Syntax 2

DataType [ ] variableName;variableName = new DataType[arraySize of type integer]

Example :

define an array variable called studentNum of type integerwith length indicate by user input;

int length;

int[ ] studentNum;length = input.nextInt();

studentNum = new int[length];




Syntax 3

DataType [ ] variableName = {value1, value2. value3.};

where n items automatically defined as an array length

Example :

define an array variable called keyCode of type integer thatcontains 1,6,7,3,4,2,1 as it values;

int[ ] keyCode ={1,6,7,3,4,2,1}


n items

What is the length/size of array keyCode?



For each array that has been instantiated, thereis a variable called length

The variable length contains the size of the array.

The variable length can be directly accessed in aprogram using the array name and the dotoperator.

.length

Instance Variable length



EXAMPLE 1:

int[ ] mark = new int[4];System.out.println(the size of marks array is+ mark.length);

OUTPUT:the size of marks array is

EXAMPLE 2:int[ ] snakeLocation = {10,23,34,49,66,83,86,90,95,99};System.out.println(the size of array snakeLocation is+ snakeLocation.length);

OUTPUT:the size of snakeLocations array is

length Example

10

4

1 2 3 4 5 6 7 8 9 10

4mark.length

10snakeLocation.length



Using loops to step through elements in array andperform the operations.

for (i = 0; i < list.length; i++)

System.out.print(list[i] + " ");

Processing One DimensionalArray

int [] list = new int [100];

int i;

declarations

for (i=0;i< list.length;i++)

list[i] = input.nextInt();

Using for loop to assign an input into the array

for (i=0;i< list.length;i++)

System.out.println(list[i] + );

Using for loop to display all elements in array



for (index = 0; index < sales.length;

index++)

sales[index] = 10.0;

sales[2]=16.0;

double[] sales = new double[4];

Common Operation onArray (1)

Initialize an array to a specific value



for (index = 0; index < sales.length;index++)

sales[index] = 10.0;

sales[2]=16.0;

double[] sales = new double[4];


Initialize an array to a specific value

sales

?

?

?

?

index sales.length

4 true

sales[0]=10.0

[0]

0

[1]

[2]

[3]

10.0

1 false

sales[1]=10.0

10.0

2

sales[2]=10.0

10.0

3

sales[3]=10.0

10.0

4

16.0



for (index = 0; index < sales.length; index++){

System.out.print(Total Sales for Month +(index+1)+ :);

sales[index] = input.nextDouble();

}


Read data into an array



for (index = 0; index < sales.length; index++){

System.out.print(Total Sales for Month +(index+1)+ :);

sales[index] = input.nextDouble();

}

0 10.0

10.0

16.0

10.0

1

2

3

sales


Read data into an array

Total Sales for Month 1 :

0 4< true

15.7

13.015.7

1

Total Sales for Month 4 :

Total Sales for Month 2 :19.7

19.7

2

Total Sales for Month 3 : 0.57

0.57

3

13.0

4 false


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System.out.println(Month + + Total Sales);

for (index = 0; index < sales.length; index++)

System.out.println((index+1) + +sales[index]");


Print the contains of the array

0

1

2

3

sales

15.7

19.7

0.57

13.0

Month Total Sales

1 15.7

2 19.7

3 0.574 13.0


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System.out.println(Month + + Total Sales);


System.out.println((index+1) + +sales[index]");


Print the contains of the array

0

1

2

3

sales

15.7

19.7

0.57

13.0

Month Total Sales


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sum = 0;


sum = sum + sales[index];

if (sales.length != 0)average = sum / sales.length;

else

average = 0.0;


Find sum and average of array

0

1

2

3

sales

15.7

19.7

0.57

13.0

sum

015.735.435.9748.97

average

12.2425


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sum = 0;


sum = sum + sales[index];

if (sales.length != 0)average = sum / sales.length;

else

average = 0.0;


Find sum and average of array

0

1

2

3

sales

15.7

19.7

0.57

13.0

false

sum

0

0 4< true

15.7

1

35.4

2

35.97

3

48.97

4

average

true

12.2425

48.97/4


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maxIndex = 0;


if (sales[maxIndex] < sales[index])maxIndex = index;

largestSale = sales[maxIndex];


Determining largest element in array

0

1

2

3

sales

15.7

19.7

0.57

13.0

largeSale 19.7


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maxIndex = 0;


if (sales[maxIndex] < sales[index])maxIndex = index;

largestSale = sales[maxIndex];


Determining largest element in array

0

1

2

3

sales

15.7

19.7

0.57

13.0

largeSale

1

maxIndex 0

< 4 true

19.715.7 true< false

1

23

0.5719.7 13.0

4 false

19.7


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The System.arraycopy() method

//original array

int ori[] = {1,2,3,4,5,,6};

//destination array

int dest[] = {10,9,8,7,6,5,4,3,2,1};

//copy all of the ori array to the dest array,

//starting with index 0System.arraycopy(ori,0,dest,0,ori.length);

//result

dest has the following contents 1,2,3,4,5,6,4,3,2,1


Copying Arrays


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An array is in bounds if:

0


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Array Index Out of Bounds(2/2)


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Relational Operators Arrays

int[] listA = new int[3];

int[] listB = new int[3];

if (listA == listB)

...

The expression listA == listB determines if the values

oflistA and listB are the same, thus determining

whether listA and listB refer to the same array.

To determine whether listA and listB contain the same

elements, you need to compare them element by element.

Relational Operator andArray (1/2)


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int[] listA = new int[4];

int[] listB = new int[3];

if (listA == listB)

listB = listA;

if(listA == listB)

Relational Operator andArray (2/2)

0

1

2

3

listA

15.7

19.7

0.57

13.0

0

1

2

listB

15.7

19.7

0.57

false

true


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Arrray of arrays

int twoDim[] = new int [4][];

twoDim[0] = new int[2];



Multi DimensionalArray

twoDim[0]

twoDim

01

34

1901

2

19

01

2

23

19

0

twoDim[1]twoDim[2]

twoDim[3]twoDim[1][1]


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write a program that accept 10 student

marks, calculating mark average, and then

print out number of students that get

more than mark average.

Example of Array Usage (1)


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1. start2. Get student mark

1. Repeat 3 times1. Get student mark and store in array

3. Calculate total mark1. While not end of array

1. Get element in the array2. Add the element to the sum

4.

Calculate average mark1. Average = sum / size of array5. Calculate number of student over average

1. While not end of array1. Get element in array2. Compare element with the average

1. If greater or equal than1. Increase numberOf StudentoverAverage by 1

6. Display Result7. End

Example of Array Usage (1/7)


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//1.start

import java.util.Scanner;public class StudentOverAverage {

public static void main(String[] args) {

//declaration

int[] mark = new int[3];int sum = 0;

int index ;

int average = 0;

int numberOfStudentOverAverage=0;

Scanner input = new Scanner (System.in);



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//2. Get student mark

// 1. Repeat 3 times// 1.Get student mark and store in array

for (index=0;index < mark.length;index++){

System.out.println(Enter Marks + (index+1));mark[index] = input.getInt();

}



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//3. Calculate total mark

// 1.While not end of array// 1.Get element in the array

// 1.Add the element to the sum

for (index=0;index < mark.length;index++){sum = sum + mark[index]

}



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//4.Calculate average mark

// 1.Average = sum / size of array

average = sum / mark.length;



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//5. Calculate number of student over average

// 1. While not end of array// 1. Get element in array

// 1. Compare element with the average

// 2. If greater or equal than

// 1.Increase

// numberOfStudentoverAverage by 1

for (index=0;index < mark.length;index++){

if (mark[index] >= average)

numberOfStudentOverAverage++;

}



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//6. Display Result

System.out.println(Number of student over

avegare are: + numberOfStudentOverAverage );

//7. end

}

}



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Case Study

100 students were asked to rate the

quality of the food in the student

cafeteria on a scale of 1 to 10 (1 means

awful and 10 means excellent). Based on

the response,1. summarize the result of the poll.

eq:

Rank Frequency Histogram

1 12 ************

2 5 *****

2. Calculate the Min, mode and median.

COMPUTER PROGRAMMING (TMK 3102) LECTURE NOTES 9

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