LAB 9 Arrays. Topics. Array of data types Accessing array elements Initializing array elements

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1 LAB 9 Arrays Topics Array of data types Accessing array elements Initializing array elements Array of data types An array is an indexed collection of objects, all of the same type. We can declare a C# array with the following syntax: type[] array_name; For example: int[] myintarray; Actually, here we have not declared an array yet. Technically, we are declaring a variable (myintarray) that will hold a reference to an array of integers. The square brackets ([]) tell the C# compiler that we are declaring and array, and the type specified the type of the elements it will contain. In the above example, myintarray is an array of integers. We can instantiate an array using the new keyword. For example: myintarray = new int[5]; This declaration creates and initializes an array of five integers, all of which are initialize to the value 0. It is important to distinguish between the array itself (which is the collection of elements) and the elements of the array. myintarray is the array (or, more accurately, the variable that hold the reference to the array); its elements are five integers it hold. Accessing array elements We access elements of an array using the index operator ([]). Arrays are zero-based, which means that the index of the first element is always 0 in this case, myintarray[0]. Arrays are objects and thus have properties. One of the more useful of these is Length, which tell us how many objects are in an array. Array objects can be indexed from 0 to Length-1. That is, if there are five elements in and array, their indexes are 0, 1, 2, 3, 4. The example 1 illustrates the usage of a simple array of integer. In this example, a class named OneDimArray is a blueprint for creating a simple array of five integers. In the Main method, we first instantiate two objects, i.e., a and b, both holds the arrays of five integers. We then access the elements in the array a using a.myintarray[i], and use the property Length to refer to the number of elements in that array. For the second array b, we call the method Power3 to initialize all of its elements, and employ the method PrintArray to write out its elements. The foreach looping statement allows us to iterate through all the elements in an array. Notice that a and b in this example are not the same array. Computer & Programming: Arrays 1/9 Powered by MIKE TM

2 //Example 1 namespace MyArray public class OneDimArray int[] myintarray; const int dim = 5; OneDimArray () myintarray = new int[dim]; static void Power3 (OneDimArray t) for (int i=0; i<dim; i++) t.myintarray[i]=i*i*i; static void PrintArray (OneDimArray t) int i=0; foreach (int j in t.myintarray) Console.WriteLine("myIntArray[0] = 1", i++, j); public static void Main() OneDimArray a = new OneDimArray(); OneDimArray b = new OneDimArray(); //one dimension array a for (int i=0; i<dim; i++) a.myintarray[i] = i*i; for (int i=0; i<a.myintarray.length; i++) Console.WriteLine("myIntArray[0] = 1", i, a.myintarray[i]); //another one dimension array b Power3(b); Console.WriteLine("Now,"); PrintArray(b); Initializing array elements It is possible to initialize the contents of an array at the same time it is instantiated by providing a list of values delimited by curly braces (). C# provides a longer and a shorter syntax like these: int[] myintarray = new int[5] 2, 4, 6, 8, 10; int[] myintarray = 2, 4, 6, 8, 10; There is no practical difference between these two statements, and most programmers will use the shorter syntax. However, in some rare circumstances we have to use the longer syntax specifically, if the C# compiler is unable to infer the correct type for the array. Reader should type and debug all the example codes found in this document to examine the output. Computer & Programming: Arrays 2/9 Powered by MIKE TM

3 Exercise : namespace Exercise1 class Fibonacii int[] fib; int num = 0; Console.Write ("Enter the number of terms: "); num = Int32.Parse (Console.ReadLine ()); fib = new int[num]; for (int i=0; i<fib.length; i++) fib[i] = fib[i-1] + fib[i-2]; for (int i=0; i<fib.length; i++) Console.Write ("0 ", fib[i]); 1.1 Run the above program with input 1. What happens and why? 1.2 Replace the statement in line 16 with the following statements. Try running the program again with the inputs 1, 2, 5, 10 and 20, respectively, for each run, and then re-examine the results. if ((i==0) (i==1)) fib[i] = 1; else fib[i] = fib[i-1] + fib[i-2]; Input Output 1.3 According to the outputs from 1.2, what does the above program do? Computer & Programming: Arrays 3/9 Powered by MIKE TM

4 Exercise : : : namespace Exercise2 class CountLetter public const int ALPHASIZE = 26; public const int DIGITSIZE = 10; int[] digitarray = new int[digitsize]; int[] alphaarray = new int[alphasize]; int other = 0; string input = ""; Console.Write ("Enter a string or a sentence: "); input = for (int i=0; i<input.length; i++) if ((input[i] >= '0') && (input[i] <= '9')) digitarray[input[i] -'0']++; else if ((input[i] >= 'a') && (input[i] <= 'z')) alphaarray[input[i] -'a']++; else other++; for (int i=0; i<digitarray.length; i++) if (digitarray[i]!= 0) Console.WriteLine("There are 0 digits of 1.", digitarray[i], (char)('0' +i)); for (int i=0; i<alphaarray.length; i++) if (alphaarray[i]!= 0) Console.WriteLine("There are 0 letters of 1.", alphaarray[i], (char)('a' +i)); if (other!= 0) Console.WriteLine("There are 0 other characters.", other); Console.ReadLine (); 2.1 Run the program with input string hello world 555 What is the output of the program? Computer & Programming: Arrays 4/9 Powered by MIKE TM

5 2.2 According to the output in 2.1, what does the above program do? 2.3 Try another input Hello WORLD 555, how does the output differ from the output in 2.1? 2.4 Rewrite the above program to make the program count an uppercase letter as a lowercase one. For example, one A and one a will be counted as two a. Write the part of the changed code below. Computer & Programming: Arrays 5/9 Powered by MIKE TM

6 Exercise : namespace Exercise3 class DecToHex const int BASE = 16; char[] table = '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'; int number = 0; string s = ""; Console.Write("Enter number: "); number = Int32.Parse(Console.ReadLine()); while (number>0) s = table[number % BASE] + s; number /= BASE; Console.WriteLine("Output = 0", s); 3.1 Run the program with the input 234, what is the output of the program? 3.2 Modify the above program to convert decimal numbers into octal (base 8) ones. Computer & Programming: Arrays 6/9 Powered by MIKE TM

7 Exercise : : : namespace Exercise4 class CalSquare static void getinput (int[] n) for (int i=0; i<n.length; i++) Console.Write("Enter num0: ", i+1); n[i] = Int32.Parse(Console.ReadLine()); static void printoutput (int[] n) Console.Write("Output = "); for (int i=0; i<n.length; i++) Console.Write("0 ", n[i]); Console.WriteLine(); static void calsquare (int[] n, int[] s) s = new int[n.length]; for (int i=0; i<n.length; i++) s[i] = n[i] * n[i]; const int SIZE = 5; int[] num = new int[size]; int[] sqr = new int[size]; getinput(num); Console.Write("num >> "); printoutput(num); calsquare(num, sqr); Console.Write("sqr >> "); printoutput(sqr); 4.1 Run the program with five inputs: 1, 2, 3, 4, and 5. What is the output of the program? 4.2 Replace the method declaration in line 20 as follows: static void calsquare (int[] n, out int[] s) And replace the statement in line 36 as the following statement: calsquare (num, out sqr) Then try running the program again with same inputs: 1, 2, 3, 4, and 5. What is the output of the program? Computer & Programming: Arrays 7/9 Powered by MIKE TM

8 4.3 Why does the output in 4.1 differ from the one in 4.2? Exercise The following program takes five numbers as user input. It then finds the minimum value, maximum value, as well as computes the average and standard deviation Complete all the blank areas of this program. (You must not change other contents of the program) Each method is defined to operate as follows: getinput gets a list (l ) of input from user. findmin returns the minimum value in the list l. findmax returns the maximum value in the list l. CalAvg CalSD returns the average value of the list l as returns the standard deviation of the list l as namespace Exercise5 class mylist static void getinput(int[] l) for (int i=0; i<l.length; i++) Console.Write("Input: ", i+1); l[i] = Int32.Parse(Console.ReadLine()); findmin ( ) l[ i] i x 1. n Computer & Programming: Arrays 8/9 Powered by MIKE TM n n 2 ( l[ i] x) i1 S. D. n.

9 20: : : : : : 7 7 const int SIZE = 5; int[] list = new int[size]; findmax ( ) calavg ( ) calsd ( ) getinput(list); Console.WriteLine("Min: 0", findmin( )); Console.WriteLine("Max: 0", findmax( )); Console.WriteLine("Avg: 0", calavg( )); Console.WriteLine("SD: 0", calsd( )); Computer & Programming: Arrays 9/9 Powered by MIKE TM