Thanachat Thanomkulabut Arrays Thanachat Thanomkulabut

Introduction If you want to declare variable for store scores of all students in 204111 course If you want to find total of scores 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];

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

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

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;

Array Declaration & Creation Format I <type> [] <name>; <name> = new <type>[<num-elts>]; Format II <type> [] <name> = new <type>[<num-elts>]; double[] score; score = new double[5]; double[] score = new double[5];

Array Declaration & Creation double[] score; score = new double[5]; score id 1 2 3 4

Array Declaration & Creation & Initialization Format I <type> [] <name> = new <type>[num-elts] {<value-lists>}; int [] arrayA = new int[3] {3, 6, 9}; Format II new <type>[] {<value-lists>}; int [] arrayA = new int[] {3, 6, 9}; Format III <type> [] <name> = {<value-lists>}; int[] arrayA = {3, 6, 9};

Array Declaration Example Declaration only Declaration with creation Declaration with initialization int [] ai; int [] ai = new int[5]; int [] ai = new int[5] {1, 2, 3, 4, 5}; int [] ai = {1, 2, 3, 4};

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

Self test I Declare ,Create and Initialize following array Array I 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];

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

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 IIII char[] text = new char[]{'c','o','m'}; Format IIII char[] text = {'c','o','m'};

Accessing Array Elements Supply an integer index for accessing array elements indexes are zero-based int [] score = new int[4]; 1 2 3 score Run time 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

Example1 Initial 0 value for every elements of array (assume length of array is 6) Show all value in each elements of array (assume length of array is 6) for(int i=0;i<6;i++) score[i] = 0; for(int i=0;i<6;i++) Console.WriteLine (“Score{0} = {1}”,i+1,score[i]);

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

Example2 Initial 0 value for every elements of array (assume length of array is 6) Show all value in each elements of array (assume length of array is 6) for(int i=0;i<6;i++) score[i] = 0; for(int i=0;i<score.Length;i++) for(int i=0;i<6;i++) Console.WriteLine (“Score{0} = {1}”,i+1,score[i]); for(int i=0;i<score.Length;i++)

Output Example3 4 Month4 has 30 days. 1 2 3 4 5 6 7 8 9 10 11 month This program will 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 monthday 4 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 This program will reports the number of days in a given month. //assume Feb have 28 days

Example24 Write the program for calculate sumation of n number Monitor 1 2 3 Input n: 4 16 3+5+1+7 3 5 1 7 3 5 1 Write the program for calculate sumation of n number 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); }

Self Test I Write a program for calculating summation of square (5 numbers, with array) 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);

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); }

String in each elements can 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’;  String in each elements can read only

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

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

foreach 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++; }

foreach 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++; }

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

Self test IV Write the Program to recieve n data & find max value of that data. Program Process Recieve “n” for check amount of data Recieve each number and collect it to each element in array Find max value of all data

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);

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

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: 11 14 15

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

Self test V 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;

Self Test V 5 4 7 -1 -8 2 3 mynum arr id 1 2 3 4 static void Main(){ 1 2 3 4 5 4 7 -1 -8 2 3 mynum arr 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; Output 5 0 7 -8 3

Example 5 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

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

Pass by Value arr id 1 2 5 4 -1 mynum arr id 1 2 10 13 15 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]); mynum arr id 1 2 10 13 15 Output Before mynum[0] = 4 In Change arr[0] = 10 After mynum[0] = 5

Pass by Reference mynum arr id 1 2 5 4 -1 mynum arr id 1 2 10 13 15 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(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

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];

Multi-dimensional Array (introduction) 1 2 3 4 50 score 1 2 3 4 50 score0 score1 1 2 score2 9 score9 double[] score0 = new double[50]; double[] score1 = new double[50]; double[] score2 = new double[50]; double[] score9 = new double[50];

Multi-dimensional Array’s declaration <type> [] <name>; int [] score; Multi-dimensional 2 Dimension <type> [ , ] <name>; int [ , ] score; 3 Dimension <type> [ , , ] <name>; int [ , , ] score;

Multi-dimensional Array’s creation score 1 Dimension <name> = new <type>[<num-elts>]; score = new int[4]; 2 Dimension <name> = new <type>[<dim1>,<dim2>]; score = new int[4,2]; 3 Dimension <name> = new <type>[<dim1>,<dim2>,<dim3>]; score = new int[4, 2, 3]; score score

Multi-dimensional Array’s 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

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

Selftest VI 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'} };

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

Example 6 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

Student 1 score1= score2= Student 2 Student 3 Student 4 3 8 6 7 10 9 Example 6 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

Example 6 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;

score 1 2 3 8 6 7 10 9 Self test VI From example 6, write the partial program to find sumation 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);

score 1 2 3 8 6 7 10 9 Self test VII From example 6, 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);

score 1 2 3 8 6 7 10 9 Self test VIII From example 6, 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);

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

Any question?