C#: Statements and Methods Based on slides by Joe Hummel

2 UCN Technology: Computer Science – 2014 Contents “With regards to programming statements and methods, C# offers what you would come to expect from a modern OOPL…” Statements Methods

3 UCN Technology: Computer Science – 2014 Part 1 Statements

4 UCN Technology: Computer Science – 2014 Statements in C# Assignments Sub routines and functions Conditionals –if, switch Iteration –for, while, do-while (Uncontrolled) Control Flow –return, break, continue, goto

5 UCN Technology: Computer Science – 2014 Examples x = obj.foo(); if (x > 0 && x < 10) count++; else if (x == -1)... else {... } while (x > 0) {... x--; } for (int k = 0; k < 10; k++) {... }

6 UCN Technology: Computer Science – 2014 Other Statements C# also includes… –iteration over a data structure (Collection) using foreach –namespace imported using using

7 UCN Technology: Computer Science – 2014 foreach Specialised foreach loop for sweeping through collections, e.g. array –Reduces the risk for indexing errors –Allows only read only access to elements int[] data = { 1, 2, 3, 4, 5 }; int sum = 0; foreach (int x in data) { sum += x; } foreach typevaluecollection

8 UCN Technology: Computer Science – 2014 using using directive provides access to classes in a namespace without pre-fixing // before Workshop.Customer c; c = new Workshop.Customer("joe hummel", 94652); //after using Workshop; Customer c; c = new Customer("joe hummel", 94652); namespace Workshop { public class Customer {. } public class Product {. }

9 UCN Technology: Computer Science – 2014 Example using directives in the top of the file /* main.cs */ using System; using Workshop; public class App { public static void Main() { Customer c; c = new Customer("joe hummel", 94652); Console.WriteLine( c.ToString() ); } namespace Workshop { public class Customer {. } public class Product {. }

10 UCN Technology: Computer Science – 2014 Part 2 Methods…

11 UCN Technology: Computer Science – 2014 Types of methods Classes may define 2 types of methods: –instance –static Instance methods can only be applied to instances (objects) of the class. So an object must be created before the method can be used. Static methods may be called using the class name

12 UCN Technology: Computer Science – 2014 Example The Array class in FCL –fully-qualified name is System.Array namespace System { public class Array { public int GetLength(int dimension) {... } public static void Sort(Array a) {... }. } instance method (no static modifier) static method (static modifier)

13 UCN Technology: Computer Science – 2014 Method call Method call (Array class): /* main.cs */ using System; public class App { public static void Main() { int[] data = { 11, 7, 38, 55, 3 }; Array.Sort(data); for (int i=0; i<data.GetLength(0); i++) Console.WriteLine(i + ": " + data[i]); }

14 UCN Technology: Computer Science – 2014 Other static methods that may come handy… using System; public class Calculator { public static void Main() { string input, output; int a, b, sum; Console.Write("Enter first integer: "); input = Console.ReadLine(); a = Convert.ToInt32(input); Console.Write("Enter second integer: "); input = Console.ReadLine(); b = Convert.ToInt32(input); sum = a + b; output = String.Format("{0} + {1} = {2}", a, b, sum); Console.WriteLine(output); } Adding two integers and printing the sum:

15 UCN Technology: Computer Science – 2014 Summing Up All the usual statements (known from Java), and a few new ones –assignment, if, for, while, foreach, using Two types of methods –instance methods, needs an object –static methods, may be called on the class