ARRAYS

Adopted from Thanomkulabut’s experiences.

Brushed up by MikeLab.Net Factory @KU.

01204111 Computer & Programming01204111 Computer & ProgrammingGroup 350-352Group 350-352Dept. of Computer EngineeringDept. of Computer EngineeringKasetsart UniversityKasetsart University

Version 2012

Review

An array is an indexed An array is an indexed collectioncollection of objects, of objects, all of the all of the same typesame type

Array declaration

2

double[] score;score = new double[5];

score

double[] score;score = new double[5]{1,2,3,3,5};

1 2 3 4 5

score

Review (2)3

Declaration onlyint [] ai;

Declaration & creationint [] ai = newnew int[4];

Declaration & creation & initialization

int [] ai = newnew int[4] {1, 2, 3, 4};

int [] ai = newnew int[] {1, 2, 3, 4};

int [] ai = {1, 2, 3, 4};

Review (3)

Access array elements

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intint [] score = [] score = newnew intint[4][4];;

1100 22 33scorescore

score[0] = -3;score[0] = -3;score[2+1] = 7;score[2+1] = 7;Score[3-1] = score[0]+score[3]Score[3-1] = score[0]+score[3]Console.WriteLine(score[2]);Console.WriteLine(score[2]);

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score[4] = 5;score[4] = 5;

Runtime Error!!

Arrays Concept5

Array is a reference data type. Reference variables are used to refer to

the data, not the data themselves.

double[] score;score = new double[5];

Create Label

Reserve Memory

id 0 1 2 3 4

score

Arrays with Methods :Example1

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class AM { static void Main(){ int[] Arr = {1, 4, 5}; Console.WriteLine (“1:{0} {1} {2}”,Arr[0],Arr[1],Arr[2]); Add10(Arr); Console.WriteLine (“2:{0} {1} {2}”,Arr[0],Arr[1],Arr[2]); }

static void Add10(int[] micky){ for(int i=0;i<micky.Length;i++) micky[i] += 10; }}

id 0 1 2

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541

1: 1 4 5Output

Arr

micky

2: 11 14 15

Arrays with Methods :Example2

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static void Main(){ char[] data; data = ReadArray(4); showArray(data);}static char[] ReadArray(int N){ char[] info = new char[N]; for(int i=0;i<N;i++) info[i] = char.Parse(Console.ReadLine()); return info;}static void showArray(char[] Nobi){ for(int i=0;i<Nobi.Length;i++) Console.Write(Nobi[i]);}

N=4 id 0 1 2 3

info

Monitor

B

B

e

e

a

a

r

rinfo

data

Nobi

Bear

Self test8

What is the output of this partial program?

static void Main(){ int[] mynum; mynum = new int[5] {4,0,-1,2,3}; Change(mynum); for(int i=0; i<mynum.Length; i++) Console.Write("{0} ",mynum[i]);}static void Change(int[] arr){ arr[0] = 5; arr[2] = 7; arr[3] = -8;}

Example 19

What is the output of this partial program?

static void Main(){ char[] name1,name2; name1 = new char[4] {'N','O','B','I'}; name2 = reverse(name1); showArr(name1); showArr(name2);}static char[] reverse(char[] arr){ int j=0; char[] arr_re = new char[arr.Length]; for(int i=arr.Length-1;i>=0;i--){ arr_re[j] = arr[i]; j++; } return arr_re;}static void showArr(char[] arr){ foreach(char x in arr) Console.Write(x); Console.WriteLine();}

NOBIIBON

Output

Pass by value VS by reference

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Pass by value We can only change the elements inside

the array

Pass by reference We can change the elements inside the

array We can change the array that variable

refers to

Pass by Value11

static void Main(){ int[] mynum; mynum = new int[3] {4,0,-1}; Console.WriteLine ("Before mynum[0] = {0}",mynum[0]); Change(mynum); Console.WriteLine ("After mynum[0] = {0}",mynum[0]);}static void Change(int[] arr){ arr[0] = 5; arr = new int[3] {10,13,15}; Console.WriteLine ("In Change arr[0] = {0}",arr[0]);}

mynum

id 0 1 24 0 -1

OutputBefore mynum[0] = 4

arr

5

id 0 1 2

13 1510

In Change arr[0] = 10After mynum[0] = 5

Pass by Reference12

static void Main(){ int[] mynum; mynum = new int[3] {4,0,-1}; Console.WriteLine ("Before mynum[0] = {0}",mynum[0]); Change(ref mynum); Console.WriteLine ("After mynum[0] = {0}",mynum[0]);}static void Change(ref int[] arr){ arr[0] = 5; arr = new int[3] {10,13,15}; Console.WriteLine ("In Change arr[0] = {0}",arr[0]);}

mynum

id 0 1 24 0 -15

OutputBefore mynum[0] = 4

arr

mynum

arr

id 0 1 2

13 1510

In Change arr[0] = 10After mynum[0] = 10

Multi-dimensional Array (introduction)

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If you want to keep score of 50 students

If each student have 10 test

double[] score = new double[50];

double[] score0 = new double[50];double[] score1 = new double[50];double[] score2 = new double[50];

double[] score9 = new double[50];

Multi-dimensional Array Declaration

1 dimension <type> []

<name>; int [] score;

Multi-dimensional

2 Dimension <type> [ , ]

<name>; int [ , ] score;

3 Dimension <type> [ , , ]

<name>; int [ , , ] score;

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Multi-dimensional Array Declaration

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1 Dimension <name> = newnew <type>[<dim size>]; score = new int[4];

2 Dimension <name> = newnew <type>[<dim1 size >,<dim2 size>]; score = new int[4,2];

3 Dimension <name> = newnew <type>[<dim1 size>,<dim2 size>,<dim3

size>]; score = new int[4, 2, 3];

scorescore

score

Multi-dimensional Array Declaration with Initialization

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1 Dimension int[] score = new int[3] {6, 1, 3};

2 Dimension int [,] score = new int[2, 3] { {1, 8, 4} , {3, 6,

9} }; int [,] score = { {1, 8, 4} , {3, 6, 9} }; int [,] score = { {1, 8, 4}

, {3, 6, 9} };

6 1 3score

1 8 4

3 6 9

score

Index of Multi-dimensional Array

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score[0,1] = 7; score[2-1 , 1+1] = 0; Console.Write(score[0,0]); for(int i = 0; i<=2 ; i++)

score[0,i] = 3; Console.Write(score.Length);

int[,] score = { {5,3,1},

{9,2,4} };

score

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1

5 3 1

9 2 4

7

0

5

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6

Selftest18

Declare, create and initialize array name Matrix

‘v’

‘a’

‘p’

‘y’

‘q’

‘s’

Matrix

‘z’‘b’

char[,] Matrix;Format I

Matrix = new char[4,2]{ {'v','a'}, {'y','q'}, {'p','z'}, {'s','b'} };

Array.GetLength()19

Get numbers of ROW in ARRAY arrayname.GetLength(0); score.GetLength(0);

Get numbers of Column in ARRAY arrayname.GetLength(1); score.GetLength(1);

Get numbers of all elements in ARRAY arrayname.Length; score.Length;

score

0 1 20

1

5 3 1

9 2 4

2

3

6

Example 220

Write the program to get score from 4 students (each student has 2 test)

Student 1score1=score2=Student 2score1=score2=Student 3score1=score2=Student 4score1=score2=

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810

97

Example 221

Write the program to get score from 4 students (each student has 2 test)

double[,] score = new double[4,2];for(int i=0;i<score.GetLength(0);i++){ Console.WriteLine("Student {0}",i+1); for(int j=0;j<score.GetLength(1);j++) { Console.Write("score{0} = ",j+1); score[i,j] = double.Parse(Console.ReadLine()); } Console.WriteLine();}

Student 1score1=score2=

Student 2score1=score2=

Student 3score1=score2=

Student 4score1=score2=

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67

810

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scorscoree0 1

0

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Example 2 with Method

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static double[,] ReadArray2(int row, int col){ double[,] score = new double[4,2]; for(int i=0;i<score.GetLength(0);i++){ Console.WriteLine("Student {0}",i+1); for(int j=0;j<score.GetLength(1);j++){ Console.Write("score{0} = ",j+1); score[i,j] = double.Parse(Console.ReadLine());

} Console.WriteLine(); } return score;}

static void Main(){ double [,] arr; arr = ReadArray2(2,4);}

Self test23

From previous example, write the partial program to find summation of all scores of all students

double sum = 0;for(int i=0;i<score.GetLength(0);i++){ for(int j=0; j<score.GetLength(1); j++){ sum += score[i,j]; }}Console.WriteLine("Sumation = {0}",sum);

scorscoree0 1

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Self test24

From previous example, write the partial program to find average of scores of all students in first test

scorscoree0 1

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double sum = 0;for(int i=0;i<score.GetLength(0);i++){ sum += score[i,0];}double avg = sum/score.GetLength(0);Console.WriteLine ("Average of First test = {0}",avg);

Self test25

From previous example, write the partial program to find average scores of all test of last student

scorscoree0 1

0

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double sum = 0;for(int j=0;j<score.GetLength(1);j++){ sum += score[3,j];}double avg = sum/score.GetLength(1);Console.WriteLine ("Average of last student = {0}",avg);

How to find Array’s #dimension?

By property Rank

int [] matrix = new int[5];int [] matrix = new int[5];

Console.WriteLine(matrix.Console.WriteLine(matrix.RankRank););

int [,,] matrix = new int[5,2,3];int [,,] matrix = new int[5,2,3];

Console.WriteLine(matrix.Console.WriteLine(matrix.RankRank););

int [,] matrix = new int[5,2];int [,] matrix = new int[5,2];

Console.WriteLine(matrix.Console.WriteLine(matrix.RankRank););

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