1. Thanachat Thanomkulabut
Array 1
Thanachat Thanomkulabut

2. Outline Introduction Declaration, Creation, Initialization, Access
Length of Array
Examples
foreach

3. Introduction
If you want to declare variable for store scores of 700 students in course,
If you want to find total score,
int s1, s2, s3, s4, s5, ... , s700;
int[] s = new int[700];
int total=0;
total = s1 + s2 + s3 + s s700;
int total=0;
for(int i=0; i<700;i++) total += s[i];

4. What is Array?
An array is an indexed collection of objects, all of the same type 1 2 3 4 5 6

5. Overview of Array We create arrays using new command.
Array elements start with index 0.
Array “a” with 6 elements: a[0], a[1], ... , a[5].
Each element in the array behaves like standard variable.

6. Outline Introduction Declaration, Creation, Initialization, Access
Length of Array
Examples
foreach

7. Array Declaration Declare Array Declare variable Syntax Syntax int x;
Name : A
Type : int
Syntax
<type> [] <name>;
Declare variable
Name : x
Type : int
Syntax
<type> <name>;
int x;
int [] A;

8. Array Creation Array differs from ordinary variable
Array can hold multiple values while ordinary variable holds only one.
We need to reserve how many values array will hold.
Reservation = Array Creation

9. Array Declaration & Creation
Format I
<type> [] <name>;
<name> = new <type>[<numElements>];
Format II
<type> [] <name> = new <type>[<numElements>];
double[] score;
score = new double[5];
double[] score = new double[5];

10. Array Declaration & Creation
double[] score;
score = new double[5];
score

11. Array Declaration & Creation & Initialization
Format I
<type> [] <name> =
new <type>[numElements] {<valueList>};
int [] arrayA = new int[3] {3, 6, 9};
Format II
<type> [] <name> = new <type>[] {<valueList>};
int [] arrayA = new int[] {3, 6, 9};
Format III
<type> [] <name> = {<valueList>};
int[] arrayA = {3, 6, 9};

12. Summary 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};

13. Self Test I Declare, Create and, Initialize the following array
Name : times
Type : array of double
Length : 5
Initial value : None
Format I
double[] times;
times = new double[5];
Format II
double[] times = new double[5];

14. Self Test II Name : text Type : Array of char Length : 3
Declare, Create and, Initialize the following array
Name : text
Type : Array of char
Length : 3
Initial value : 'c', 'o', 'm'

15. Self Test II Format I char[] text; text = new char[3]{'c','o','m'};
Format II
char[] text;
text = new char[]{'c','o','m'};
Format III
char[] text = new char[3]{'c','o','m'};
Format IV
char[] text = new char[]{'c','o','m'};
Format V
char[] text = {'c','o','m'};

16. Access Array Elements ID 1 2 3 score int [] score = new int[4];
Supply an integer index for accessing array elements
Indexes are zero-based
int [] score = new int[4]; ID 1 2 3
score

17. Access Array Elements (2)
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

18. More Examples 1 2 3 4 5 score 1 2 3 score 5 6 7 9
int [] score = new int[6]; 1 2 3 4 5
score
int [] score = new int[4] {5,6,7,9}; 1 2 3
score 5 6 7 9

19. Outline Introduction Declaration, Creation, Initialization, Access
Length of Array
Examples
foreach

20. Example
Initial 0 value for every element of array (assume length of array is 6)
Show all values in each element of array (assume length of array is 4)
for(int i=0;i<6;i++)
score[i] = 0;
for(int i=0;i<4;i++)
Console.WriteLine
(“Score{0} = {1}”,i+1,score[i]);

21. How to find length of array?
By property Length
int[] matrix = new int[5];
Console.WriteLine(matrix.Length); 5
By method GetLength()
int[] matrix = new int[7];
Console.WriteLine(matrix.GetLength(0)); 7

22. Example
Initial 0 value for every element of array (assume length of array is 6)
Show all values in each element of array (assume length of array is 4)
for(int i=0;i<6;i++)
score[i] = 0;
for(int i=0;i<score.Length;i++)
for(int i=0;i<4;i++)
Console.WriteLine
(“Score{0} = {1}”,i+1,score[i]);
for(int i=0;i<score.Length;i++)

23. Outline Introduction Declaration, Creation, Initialization, Access
Length of Array
Examples
foreach

24. Output
Example 4
Month4 has 30 days. 1 2 3 4 5 6 7 8 9 10 11
month
This program report the number of days in a given month. //assume Feb have 28 days 31 28 31 30 31 30 31 31 30 31 30 31
monthday 4
static void Main(){ }
int[] monthday = {31,28,31,30,31,30, ,31,30,31,30,31};
int month =
int.Parse(Console.ReadLine());
Console.Write(“Month{0} has {1} days.”,
month,monthday[month-1]); 4 3
This program reports the number of days in a given month. //assume Feb have 28 days

25. Example 2 Write a program to calculate summation of n numbers Monitor1 2 3
Input n: 4 16 3 5 1 7 3 5 1
Write a program to calculate summation of n numbers 7
Sum = 16
static void Main(){
Console.Write("Input n: ");
int n = int.Parse(Console.ReadLine());
int[] num = new int[n];
for(int i=0;i<num.Length;i++)
num[i] = int.Parse(Console.ReadLine());
int sum = 0;
sum = sum+num[i];
Console.WriteLine("Sum = {0}",sum); }

26. Element in string can be read only
Output
String 1 2 3 4 B
name B o s s a o
String is array of chars.
string name = “Bossa”;
Console.WriteLine(name[0]);
Console.WriteLine(name[4-3]);
name[4] = ‘m’; 
Element in string can be read only

27. String Counting number of letter ‘a’ in a sentence count i I words a m1 2 3 4 5 6 7 8 9 10 I
words a m a m a n
Counting number of letter ‘a’ in a sentence
string words = “I am a man”; int count = 0; int i = 0; while (i < words.Length) 
{      if (words[i] == 'a')           count++;      i++; } Console.WriteLine("Number of letter \'a\' = {0}", count);
= 10
X False
Output
count
Number of letter ‘a’ = 3 3 2 1

28. String: Counting number of each letter in a sentence
string words = "I am a man"; int[] count = new int[26]; int value, i = 0;
// convert all letters to uppercase first words = words.ToUpper(); while (i < words.Length) {       value = words[i]-‘A';    if (value<26 && value>=0)          count[value]++;    i++; }
// loop for printing results
for(int j=0; j<26;j++)
{ if (count[j]!=0)        Console.WriteLine(
“{0}={1}“,
Convert.ToChar(j+65),
count[j]); }
Output
A= 3
I=1
M=2
N=1

29. Self Test III
Write a program using array to calculate summation of 5 squared numbers
4* *3 + 7*7 + 2*2 + 5*5
int a, b, c, d, e;
a = int.Parse(Console.ReadLine());
b = int.Parse(Console.ReadLine());
c = int.Parse(Console.ReadLine());
d = int.Parse(Console.ReadLine());
e = int.Parse(Console.ReadLine());
int square_sum = a*a + b*b + c*c + d*d + e*e;
Console.WriteLine("Sum of square is {0}", square_sum);

30. Self Test III static void Main(){ int[] num = new int[5];
for(int i=0;i<num.Length;i++)
num[i] = int.Parse(Console.ReadLine());
int square_sum = 0;
squre_sum += num[i]*num[i];
Console.WriteLine("Sum = {0}",square_sum); }

31. Self Test IV
Write a program to receive n numbers & find maximum value.
Process
Read value of n
Read n numbers, and store each read number in element of array one at a time
Find maximum among n numbers

32. Self Test IV static void Main(){ int n;
n = int.Parse(Console.ReadLine());
double[] data = new double[n];
for(int i=0;i<n;i++)
data[i] = double.Parse(Console.ReadLine());
double max=0;
for(int i=0;i<n;i++){
if(data[i] > max)
max = data[i]; }
Console.WriteLine("max = {0}",max);

33. Outline Introduction Declaration, Creation, Initialization, Access
Length of Array
Examples
foreach

34. Looping or Iteration in C#
while
Iteration
for
foreach
do…while

35. foreach
foreach is used to (only) read each element in an array and do some action repeatedly
foreach = “for each element in an array”
Syntax:
foreach(var_declaration in array_name)
statement;

36. Example 1 string s = Console.ReadLine(); int count = 0;
for (int i = 0; i < s.Length; i++){
if (s[i] == 'A')
count++; }
string s = Console.ReadLine();
int count = 0;
foreach (char c in s){
if (c == 'A')
count++; }

37. Example 2 int[] score = new int[5]{4,9,0,8,7}; int count = 0;
foreach (int x in score){
if(x%2 == 0)
count++; }

38. foreach is used to only read elements in array
Example 3
int[] num = new int[5]{2, 4, 5, 8, 0};
foreach( int n in num){
n += 10; } 
foreach is used to only read elements in array

39. Any question?