This document discusses methods in C# programming. It begins with an introduction to methods and their use for modularizing programs into self-contained units. It then covers defining and calling methods, including specifying return types, parameters, and access modifiers. Examples are provided of common math methods and defining custom methods to calculate taxes, add values, and find maximum values. Common errors related to method definitions and usage are also listed.

1. Methods(1)
Lecture 5
Dr. Hakem Beitollahi
Computer Engineering Department
Soran University

2.  Introduction
 Math Class Methods
 Methods
 Method Definitions
 Argument Promotion
Methods(I)— 2

3. Introdcution
 Most computer programs that solve real-world
problems are much larger than programs that
you have written yet!
 Experience has shown that the best way to
develop and maintain a large program is to
construct it from small, simple pieces, or
modules.
 Methods are the building blocks of C# and the
place where all program activity occurs.
 Divide and conquer technique
 Construct a large program from small, simple pieces
(e.g., components)
Methods(I)— 3

4. What are methods?
 Methods
 Called functions or procedures in other languages
 Allow programmers to modularize a program by
separating its tasks into self-contained units
o Statements in method bodies are written only once
 Reused from perhaps several locations in a program
 Hidden from other methods
 Avoid repeating code
o Enable the divide-and-conquer approach
o Reusable in other programs
o User-defined or programmer-defined methods
Methods(I)— 4

5. Software engineering tip
To promote software reusability, every method
should be limited to performing a single, well-defined
task, and the name of the method should
express that task effectively. Such methods make
programs easier to write, test, debug and
maintain.
A small method that performs one task is easier
to test and debug than a larger method that
performs many tasks.
Methods(I)— 5

6. Methods in C#
 C# programs are written by combining new
methods and classes
 available in the .NET Framework Class Library
(FCL)
 The FCL provides:
 mathematical calculations, string
manipulations, character manipulations,
input/output operations and so on.
 A method is invoked by a method call.
Methods(I)— 6

7. Methods in C#
 Methods (Cont.)
 A method is invoked by a method call
o Called method either returns a result or simply returns to the
caller
o method calls form hierarchical relationships
Methods(I)— 7

8. Math Class Methods
Methods(I)— 8

9. Math Class Methods (I)
 Math class methods allow the programmer to
perform certain common mathematical
calculations.
 Methods are called by writing the name of the
method, followed by a left parenthesis, the
argument and a right parenthesis.
 The parentheses may be empty, if we are calling
a method that needs no information to perform
its task.
Return a double value
 Example:
 double x = Math.Sqrt( 900.0 )
Methods(I)— 9
Argument

10. Software Engineering Observation 6.3
 It is not necessary to add an assembly
reference to use the Math class methods
in a program. Class Math is located in
namespace System, which is available
to every program.
Methods(I)— 10

11. Math Class Methods (II)
Methods(I)— 11

12. Methods(I)— 12

13. Math Class Methods (III)
Methods(I)— 13

14. Method Definitions
Methods(I)— 14

15. Method Definitions (I)
 The general form of a function is
ret-type method-name(parameter list)
{
body of the function
}
 The ret-type specifies the type of data that the method
returns.
 A method may return any type of data except an array.
 The parameter list is a comma-separated list of variable
names and their associated types that receive the values
of the arguments when the function is called.
 Methods must be declared within a class or a
structure.
Methods(I)— 15

16. Method Definitions (II)
Methods(I)— 16

17. Method Definitions (III)
 A C# method consists of two parts
 The method header, and
 The method body
 The method header has the following
syntax
<<rreettuurrnn vvaalluuee>> <<nnaammee>> ((<<ppaarraammeetteerr lliisstt>>))
 The method body is simply a C# code
enclosed between { }
Methods(I)— 17

18. Method Example
Methods(I)— 18
double computeTax(double income)
{
double taxes ;
if (income < 5000.0)
return 0.0;
taxes = 0.07 * (income-5000.0);
return taxes;
}
Function header
Function body

19. Method Definitions (IV)
 Basic characteristics of methods are:
 Return value type
o output: data type or void
 Method name
o Any legal character can be used in the name of a method.
o method names begin with an uppercase letter.
o The method names are verbs or verbs followed by adjectives or nouns.
 Method parameters
o inputs for the method
o Empty parentheses indicate that the method requires no parameters.
 Parentheses
 Block of statements
o The method block is surrounded with { } characters.
 Access level
o who can call the method
Methods(I)— 19
Execute
FindId
SetName
GetName
CheckIfValid
TestValidity

20. Method Signature
 The method signature is actually similar to
the method header except in two aspects:
 The parameters’ names may not be specified
in the function signature
 The method signature must be ended by a
semicolon
 Example Unnamed
Parameter
Semicolon
;
double computeTaxes(double) ;
double computeTaxes(double income) ;
Methods(I)— 20

21. Methods must be declared inside class
Inside class every method should be
public or private (later)
This method return nothing (void)
Define an object for calling the method
Methods(I)— 21
Calling the method

22. Method Definitions (V)
 Each method must be defined inside a class or a
struct.
 It must have a name. In our case the name is
ShowInfo.
 The keywords that precede the name of the
method are access specifier (public) and the
return type (void).
 Parentheses follow the name of the method.
 They may contain parameters of the method.
 Our method does not take any parameters.
Methods(I)— 22

23. Method Definitions (VI)
Methods(I)— 23
static void Main()
{
...
}
This is the Main() method. It is the entry point to each console or GUI
application.
 It must be declared static.
We will see later why.
 The return type for a Main() method may be void or int.
The access specifier for the Main() method is omitted. In such a case a default
one is used, which is private.

24. Method Definitions (VII)
 We create an instance of the Base class.
 We call the ShowInfo() method upon the
object.
 The method is called by specifying the
object instance, followed by the member
access operator — the dot, followed by the
method name.
Methods(I)— 24
Base bs = new Base();
bs.ShowInfo();

25. Another Example
Methods(I)— 25

26. Example: Tax compute
A method to compute tax
Return type: double
An input parameter (argument) : double
Methods(I)— 26

27. Example: Tax compute
A method to get salary
Return type: double
An input parameter (argument) : string
Methods(I)— 27

28. Example: Tax compute
A method to print tax
Return type: void
An input parameter (argument) : double
Methods(I)— 28

29. Example: Tax compute
Define an object from class: ob
ob.NameofMethod
Calling the methods
Methods(I)— 29

30. More about Method parameters
Methods(I)— 30

31. Method Parameters
 A parameter is a value passed to the
method.
 Methods can take one or more
parameters.
 If methods work with data, we must pass
the data to the methods.
 We do it by specifying them inside the
parentheses.
 In the method definition, we must provide
a name and type for each parameter.
Methods(I)— 31

32. Example: Method parameters (I)
Methods should be inside a class
Methods(I)— 32

33. Example: Method parameters (II)
Method AddTwoValues
Return type: int
use the return keyword to return a
value
Input parameters: int a, int b
Methods(I)— 33

34. Example: Method parameters (III)
Method AddThreeValues
Return type: int
use the return keyword to return a
value
Input parameters: int a, int b, int c
Methods(I)— 34

35. Example: Method parameters (IV)
Define an object from class to call
methods
Calling methods
Two methods return integer, so x and
y should be integers
Methods(I)— 35

36. Methods inside the Main class (I)
 Another Example: define methods inside
the main class
Methods(I)— 36
For methods inside the main class
Access specifier: should be static

37. Methods inside the Main class (II)
 Another Example: define methods inside
the main class
No need to define an object. Directly
use the name of method to call the
method
Methods(I)— 37

38. Methods in Windows Application Forms
Methods(I)— 38

39. Methods(I)— 39

40. Methods(I)— 40

41. Common Programming Error 6.2
 Defining a method outside the braces of a
class definition is a syntax error.
Methods(I)— 41

42. Common Programming Error 6.3
 Omitting the return-value-type in a method
definition is a syntax error. If a method
does not return a value, the method’s
return-value-type must be void.
Methods(I)— 42

43. Common Programming Error 6.4
 Forgetting to return a value from a method
that is supposed to return a value is a
syntax error. If a return-value-type other
than void is specified, the method must
contain a return statement that returns a
value.
Methods(I)— 43

44. Common Programming Error 6.5
 Returning a value from a method whose
return type has been declared void is a
syntax error
Methods(I)— 44

45. Common Programming Error 6.6
 Placing a semicolon after the right
parenthesis enclosing the parameter list of
a method definition is a syntax error.
Methods(I)— 45

46. Common Programming Error 6.7
 Redefining a method parameter in the
method’s body is a syntax error.
Methods(I)— 46

47. Common Programming Error 6.9
 Passing to a method an argument that is
not compatible with the corresponding
parameter’s type is a syntax error.
Methods(I)— 47

48. Common Programming Error 6.9
 Defining a method inside another method
is a syntax error (i.e., methods cannot be
nested)
Methods(I)— 48

49.  Example: write a method to find maximum
of three double values
 Use windows application form
Methods(I)— 49

50. Methods(I)— 50

51. Methods(I)— 51

52. Methods(I)— 52