1. Arrays 01204111 Computer & Programming Group 350-352
Dept. of Computer Engineering
Kasetsart University
Adopted from Thanomkulabut’s experiences.
Brushed up by MikeLab.Net
Version 2012

2. Review Array declaration
An array is an indexed collection of objects, all of the same type
Array declaration
double[] score;
score = new double[5];
double[] score;
score = new double[5]{1,2,3,3,5};
score 1 2 3 4 5
score

3. Review (2) int [] ai; int [] ai = new int[4];
Declaration only
int [] ai;
Declaration & creation
int [] ai = new int[4];
Declaration & creation & initialization
int [] ai = new int[4] {1, 2, 3, 4};
int [] ai = new int[] {1, 2, 3, 4};
int [] ai = {1, 2, 3, 4};

4. Review (3) 1 2 3 score int [] score = new int[4];
Access array elements
int [] score = new int[4]; 1 2 3
score
Runtime Error!! -3 4 7
score[0] = -3;
score[2+1] = 7;
Score[3-1] = score[0]+score[3]
Console.WriteLine(score[2]);
score[4] = 5; 4

5. Arrays Concept id 1 2 3 4 Array is a reference data type.
Reference variables are used to refer to the data, not the data themselves.
score
Create Label
double[] score;
score = new double[5];
Reserve Memory id 1 2 3 4

6. Arrays with Methods :Example1
micky
class AM {
static void Main(){
int[] Arr = {1, 4, 5};
Console.WriteLine
(“1:{0} {1} {2}”,Arr[0],Arr[1],Arr[2]);
Add10(Arr);
(“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;
Arr id 1 2 5 4 1 15 14 11
Output
1: 1 4 5 2:

7. Arrays with Methods :Example2
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]);
data
info
Nobi
info id 1 2 3 B e a r
N=4 B e a r B e a r
Monitor

8. Self test 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;

9. Example 1 What is the output of this partial program? Output NOBI IBON
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();
What is the output of this partial program?
Output
NOBI
IBON

10. Pass by value VS by reference
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

11. Pass by Value mynum id 1 2 5 4 -1 arr id 1 2 static void Main(){1 2 5 4 -1
static void Main(){
int[] mynum;
mynum = new int[3] {4,0,-1};
Console.WriteLine
("Before mynum[0] = {0}",mynum[0]);
Change(mynum);
("After mynum[0] = {0}",mynum[0]); }
static void Change(int[] arr){
arr[0] = 5;
arr = new int[3] {10,13,15};
("In Change arr[0] = {0}",arr[0]);
arr id 1 2 10 13 15
Output
Before mynum[0] = 4
In Change arr[0] = 10
After mynum[0] = 5

12. Pass by Reference mynum arr id 1 2 5 4 -1 mynum arr id 1 21 2 5 4 -1
static void Main(){
int[] mynum;
mynum = new int[3] {4,0,-1};
Console.WriteLine
("Before mynum[0] = {0}",mynum[0]);
Change(ref mynum);
("After mynum[0] = {0}",mynum[0]); }
static void Change(ref int[] arr){
arr[0] = 5;
arr = new int[3] {10,13,15};
("In Change arr[0] = {0}",arr[0]);
mynum
arr id 1 2 10 13 15
Output
Before mynum[0] = 4
In Change arr[0] = 10
After mynum[0] = 10

13. Multi-dimensional Array (introduction)
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];

14. Multi-dimensional Array Declaration
<type> [] <name>;
int [] score;
Multi-dimensional
2 Dimension
<type> [ , ] <name>;
int [ , ] score;
3 Dimension
<type> [ , , ] <name>;
int [ , , ] score;

15. Multi-dimensional Array Declaration
score
1 Dimension
<name> = new <type>[<dim size>];
score = new int[4];
2 Dimension
<name> = new <type>[<dim1 size >,<dim2 size>];
score = new int[4,2];
3 Dimension
<name> = new <type>[<dim1 size>,<dim2 size>,<dim3 size>];
score = new int[4, 2, 3];
score
score

16. Multi-dimensional Array Declaration with Initialization
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} };
score 6 1 3
score 1 8 4 3 6 9

17. Index of Multi-dimensional Array
int[,] score = { {5,3,1},
{9,2,4} }; 1 2
score 5 3 3 7 3 1 3 1 9 2 4
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); 5 6

18. Selftest Declare, create and initialize array name Matrix Matrix
Format I
‘v’
‘a’
‘p’
‘y’
‘q’
‘s’
Matrix
‘z’
‘b’
char[,] Matrix;
Matrix = new char[4,2]{
{'v','a'},
{'y','q'},
{'p','z'},
{'s','b'} };

19. Array.GetLength() Get numbers of ROW in ARRAY
score 1 2 5 3 9 4
Array.GetLength()
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; 2 3 6

20. Example 2
Student 1
Write the program to get score from 4 students (each student has 2 test)
score1= 3
score2= 8
Student 2
score1= 6
score2= 7
Student 3
score1= 8
score2= 10
Student 4
score1= 9
score2= 7

21. Student 1
score1=
score2=
Student 2
Student 3
Student 4 3 8 6 7 10 9
Example 2
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();
score 1 2 3 3 8 6 7 8 10 9 7

22. Example 2 with Method static void Main(){ double [,] arr;
arr = ReadArray2(2,4); }
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;

23. score 1 2 3 8 6 7 10 9
Self test
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);

24. score 1 2 3 8 6 7 10 9
Self test
From previous example, write the partial program to find average of scores of all students in first test
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);

25. score 1 2 3 8 6 7 10 9
Self test
From previous example, write the partial program to find average scores of all test of last student
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);

26. How to find Array’s #dimension?
By property Rank
int [] matrix = new int[5];
Console.WriteLine(matrix.Rank); 1
int [,] matrix = new int[5,2];
Console.WriteLine(matrix.Rank); 2
int [,,] matrix = new int[5,2,3];
Console.WriteLine(matrix.Rank); 3