Array 1

1. 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 01204111 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 + s4 + ... + s700; int total=0; for(int i=0; i<700;i++) total += s[i];

4. What is Array? • An array is an indexed collectionof objects, all of the same type 0 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 variable • Name : x • Type : int • Syntax • <type> <name>; • Declare Array • Name : A • 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 =newint[4]; • Declaration & creation & initialization • int [] ai =newint[4]{1, 2, 3, 4}; • int [] ai = newint[]{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 • 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 • Supply an integer index for accessing array elements • Indexes are zero-based int [] score = newint[4]; ID 0 1 2 3 score

17. 3 0 1 2 score Access Array Elements (2) int [] score = newint[4]; Runtime Error!! -3 4 7 score[4] = 5; score[0] = -3; score[2+1] = 7; Score[3-1] = score[0]+score[3] Console.WriteLine(score[2]); 4

18. score score 5 6 7 9 More Examples int [] score = newint[6]; 3 4 5 0 1 2 int [] score = newint[4]{5,6,7,9}; 3 0 1 2

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(inti=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(inti=0;i<score.Length;i++) for(int i=0;i<4;i++) Console.WriteLine (“Score{0} = {1}”,i+1,score[i]); for(inti=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. 10 11 4 5 7 8 9 1 2 3 6 0 month • This program reports 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 • This program report the number of days in a given month. //assume Feb have 28 days 4 monthday static void Main(){ } int[] monthday = {31,28,31,30,31,30, 31,31,30,31,30,31}; int month = int.Parse(Console.ReadLine()); Console.Write(“Month{0} has {1} days.”, month,monthday[month-1]); 4 3

25. Monitor Example 2 sum 0 2 3 1 Input n: 4 3+5+1+7 0 3 5 1 7 16 3 num 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; for(int i=0;i<num.Length;i++) sum = sum+num[i]; Console.WriteLine("Sum = {0}",sum); }

26. Output String 0 1 2 3 4 B B o s s a o name • 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 i 2 3 4 10 0 1 5 6 7 8 9 I a n a m a m words • 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 1 2 3 0

28. String: Counting number of each letter in a sentence Output A= 3 I=1 M=2 N=1

29. Self Test III Write a program using array to calculatesummation of 5 squared numbers 4*4 + 3*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; for(int i=0;i<num.Length;i++) 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 foreach for do…while

35. foreach • foreach is used to (only) readeach 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(); intcount = 0; for (inti= 0; i< s.Length; i++){ if (s[i] == 'A') count++; } string s = Console.ReadLine(); intcount = 0; foreach(char c in s){ if (c == 'A') count++; }

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

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

39. Any question?