OOP with C# by Dr.hakim

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

2.  Introduction
 Math Class Methods
 Methods
 Method Definitions
 Argument Promotion
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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)
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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
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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.
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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.
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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
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8. Math Class Methods
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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 )
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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.
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11. Math Class Methods (II)
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13. Math Class Methods (III)
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14. Method Definitions
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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.
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16. Method Definitions (II)
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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 { }
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18. Method Example
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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
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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) ;
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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
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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.
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23. Method Definitions (VI)
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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.
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Base bs = new Base();
bs.ShowInfo();

25. Another Example
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26. Example: Tax compute
A method to compute tax
Return type: double
An input parameter (argument) : double
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27. Example: Tax compute
A method to get salary
Return type: double
An input parameter (argument) : string
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28. Example: Tax compute
A method to print tax
Return type: void
An input parameter (argument) : double
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29. Example: Tax compute
Define an object from class: ob
ob.NameofMethod
Calling the methods
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30. More about Method parameters
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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.
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32. Example: Method parameters (I)
Methods should be inside a class
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33. Example: Method parameters (II)
Method AddTwoValues
Return type: int
use the return keyword to return a
value
Input parameters: int a, int b
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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
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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
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36. Methods inside the Main class (I)
 Another Example: define methods inside
the main class
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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
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38. Methods in Windows Application Forms
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41. Common Programming Error 6.2
 Defining a method outside the braces of a
class definition is a syntax error.
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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.
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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.
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44. Common Programming Error 6.5
 Returning a value from a method whose
return type has been declared void is a
syntax error
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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.
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46. Common Programming Error 6.7
 Redefining a method parameter in the
method’s body is a syntax error.
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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.
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48. Common Programming Error 6.9
 Defining a method inside another method
is a syntax error (i.e., methods cannot be
nested)
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49.  Example: write a method to find maximum
of three double values
 Use windows application form
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