Lecture 11 Parameters CSE 1322 4/26/2018

What is a Method? Think of a method as a black box that contains the detailed implementation for a specific task. The method may use inputs (parameters) and may return an output with a specific type. 4/26/2019

Method Structure 4/26/2019

Method Structure 4/26/2019

Parameters and Argument Passing 4/26/2019

Parameters There are three main types of parameters: Value - passes a copy (value) of the variable to the method.  This is the default. Reference (C#)- passes a reference to the actual variable.  Marked with "ref", use this when you want to pass a value in and have any change to that value be persistent when the method is complete Out (C#) - passes a reference to the actual variable.  Marked with "out", use this when you want the method to generate a value and place it for later use in the actual variable (persists when the method is complete) Note that java passes all parameters by value. C++ uses both Call-by-reference and Call-by-value 4/26/2018

Example 1 and the output is ? static void Main(String[] args) { int a = 42; Console.WriteLine (a); // Prints 42 B (a); // Prints 51 // Call-by-value; Console.WriteLine (a); // Prints 42 } static void B (int x) // Built-in type argument passing x += 9; Console.WriteLine (x); A Call-by-value Method with C# 4/26/2018

Example 1 and the output is ? 4/26/2018

Example 1 and the output is ? static void Main(String[] args) { int a = 42; System.out.println (a); // 42 B (a); // 51 System.out.println (a); // 42 } static void B (int x) x += 9; System.out.println (x); 4/26/2018

A Call-By-Value Example with Java public class CallByValueEx2 { public static void main(String[] args) { String myname = "Mokter"; // myname is a is String reference local variable System.out.println("Initially, inside main(), Name = " + myname ); callMe(myname); System.out.println("After calling callMe(), Name = " + myname); // Look here ??!!?? System.out.println("Now, inside main(), Name = " + myname ); } static void callMe(String newname ) { // newname is String reference argument newname = "Dr. Mokter Hossain"; System.out.println("Inside callMe(), Name = " + newname ); 4/26/2018

A Call-By-Value Example with Java 4/26/2018

Example 2 and the output is ? static void Main(String[] args ) { int a = 42; Console.WriteLine (a); B (ref a); } static void B (ref int x) x += 9; Console.WriteLine (x); 4/26/2018

Example 2 and the output is ? 4/26/2018

Example 42 and the output is ? 4/26/2018

Example 3 and the output is ? The out works same as ref but it is optional to initialize in the caller method Example 3 and the output is ? static void Main(String[] args) { int a; // NOT initialized B (out a); Console.WriteLine (a); } static void B (out int x) { x = 9; Console.WriteLine (x); Source: https://www.dotnettricks.com/learn/csharp/difference-between-ref-and-out-parameters 4/26/2018

Example 3 and the output is ? 4/26/2018

Example 4 and the output is ? using System; namespace CSE1322ReviewCS{ class Program { class Z { public int y; } static void Main(String[] args) { Z myZ = new Z(); myZ.y = 42; Console.WriteLine(myZ.y); B(myZ); Console.WriteLine("Press any key to exit."); Console.ReadKey(); } static void B(Z x) { x.y += 9; Console.WriteLine(x.y); 4/26/2018

Example 4 and the output is ? class Z { public int y; } static void Main() { Z myZ = new Z(); myZ.y = 42; System.out.println (myZ.y); B (myZ); } static void B (Z x) x.y += 9; System.out.println (x.y); 4/26/2018

Example 4 and the output is ? 4/26/2018

Example 5 and the output is ? using System; class Example5 { class Z { public int y; } static void Main(String[] args) { Console.WriteLine("Example5...."); Z myZ = new Z(); myZ.y = 42; Console.WriteLine(myZ.y); B(ref myZ); Console.ReadKey(); } static void B(ref Z x) { x = new Z(); x.y = 1; Console.WriteLine(x.y); 4/26/2018

Example 5 and the output is ? 4/26/2018

Pass-by-value vs. Pass-by-reference vs. Pass-by-reference-type Be careful to note the difference between a pass-by-reference parameter and a parameter of a reference type. Use the activation stack to track local variables and how parameters of the above types affect the variables from one stack frame to the next. 4/26/2018

Overloading Methods Method overloading is the process of using the same method name for multiple methods The signature of each overloaded method must be unique The signature includes the number, type, and order of the parameters The compiler determines which version of the method is being invoked by analyzing the parameters The return type of the method is not part of the signature 4/26/2018

Overloading Methods float tryMe (int x) { return x + .375; } Version 1 float tryMe (int x, float y) { return x*y; } Version 2 result = tryMe (25, 4.32f) Invocation 4/26/2018

Overloading Operators In C#, not only can methods be overloaded, operators can be overloaded as well. Java does not allow operator overloading 4/26/2018

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Operator overloading C# enables you to overload most operators to make them sensitive to the context in which they are used. Use operator overloading when it makes an application clearer than accomplishing the same operations with explicit method calls. Class ComplexNumber overloads the plus (+), minus (-) and multiplication (*) operators to enable programs to add, subtract and multiply instances of class ComplexNumber using common mathematical notation 4/26/2018

Operator Overloading Keyword operator, followed by an operator symbol, indicates that a method overloads the specified operator. Methods that overload binary operators must take two arguments—the first argument is the left operand, and the second argument is the right operand. Overloaded operator methods must be public and static. 4/26/2018

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Overload the plus operator (+) to perform addition of ComplexNumbers 4/26/2018