Methods Session 04 Mata kuliah: M0874 – Programming II Tahun: 2010

Bina Nusantara University 3 Outline Materi Program Modules in C# Methods Definitions Value Types and Reference Types Passing Arguments: Pass-by-Value vs. Pass-by- Reference Recursion Recursion vs. Iteration

Bina Nusantara University 4 Program Modules in C# Modules in C# are called methods and classes. Programmer can write methods to define specific tasks that may be used at many points in a program. For example math class methods, allow the programmer to perform certain common mathematical calculations. To calculate and print the square root of 900.0: Console.WriteLine( Math.Sqrt ( ) );

Bina Nusantara University 5 Methods Definitions Programs contained at least one method definition (such as Main). Several motivations for modularizing a program with methods: Divide-and-conquer approach makes program development more manageable. Software reusability-using existing methods (and classes) as building blocks to create new program. To avoid repeating code in a program.

Bina Nusantara University 6 Methods Definitions With proper method naming and definition, we can create programs from standardized methods, rather than building customized code. For example, we did not have to define how to convert strings to integers-The.Net Framework Class Library already defines such methods for us.

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Bina Nusantara University 11 Value Types and Reference Types C# includes built-in value types and reference types. Value types normally represent single pieces of data, such as int or bool values. The built-in value types are the integral types (sbyte, byte, char, short, ushort, int, uint, long, and ulong), the floating-point types (float and double) and the types decimal and bool.

Bina Nusantara University 12 Value Types and Reference Types Reference types, on the other hand, refer to objects, which can contain many individual pieces of data. The built-in reference types are string and object. Programmers also can create value types and reference types. The reference types that programmers can create are classes, interfaces and delegates.

13 Passing Arguments: Pass-by-Value vs. Pass-by- Reference When an argument is passed by value, the called method receives a copy of the argument’s value. When an argument is passed using pass-by- reference, the caller gives the method the ability to access and modify the caller’s original data directly. Pass-by-reference can improve performance because it eliminates the overhead of copying large data items such as objects; However, pass-by-reference can weaken security because the called methods can modify the caller’s data.

Bina Nusantara University 14 Pass-by-Value

Bina Nusantara University 15 Pass-by-Reference

Bina Nusantara University 16 Recursion A recursive method is a method that calls itself either directly or indirectly through another method. For some problems, it is useful to have a method actually cal itself. Advantages of recursion: Game programming Artificial Intelligence Most of the mathematic functions can be presented in the form of recursion For some problems, it very easy to understand them using recursion

17 Recursion example namespace Recursion { class IterateFolders { public static void Main(string[] args) { DirectoryInfo dir = new Files\Adobe\Acrobat 5.0"); getDirsFiles(dir); } public static void getDirsFiles(DirectoryInfo d){ FileInfo [] files; files = d.GetFiles("*.*"); foreach (FileInfo file in files) { String fileName = file.FullName; String fileSize = file.Length.ToString(); String fileExtension =file.Extension; String fileCreated = file.LastWriteTime.ToString();

18 Recursion example io.WriteLine(fileName + " " + fileSize + " " + fileExtension + " " + fileCreated); } DirectoryInfo [] dirs = d.GetDirectories("*.*") foreach (DirectoryInfo dir in dirs) { io.WriteLine(" >> {0} ", dir.Name); getDirsFiles(dir); } The output will show all folders for the specified folder and list the details of each file including full path, size, extension and date created.

Bina Nusantara University 19 Recursion vs. Iteration Both iteration and recursion are based on a control structure. Iteration uses a repetition structure (such as for, while, do/while), recursion uses a selection structure (such as if, if/else or switch) Both iteration and recursion involve repetition. Iteration explicitly uses a repetition structure and recursion achieves repetition through repeated method calls. Iteration and recursion each involve a termination test. Iteration terminates when the loop-continuation condition fails and recursion terminates when a base case is recognized.

Bina Nusantara University 20 Recursion vs. Iteration Any problem that can be solved recursively also can be solved iteratively (nonrecursively). Recursive solutions also are chosen when iterative solutions are not apparent. Avoid using recursion in performance situation. Recursive calls take time and consume additional memory.

Bina Nusantara University 21 References sharpcorner.com/UploadFile/myoussef/CSharpMeth odsP_ AM/CSharpMethodsP_1.a spxhttp:// sharpcorner.com/UploadFile/myoussef/CSharpMeth odsP_ AM/CSharpMethodsP_1.a spx 4.htmlhttp:// 4.html p.aspxhttp:// p.aspx