- 1. Methods(1)Lecture 5Dr. Hakem BeitollahiComputer Engineering
DepartmentSoran University
2. Introduction Math Class Methods Methods Method Definitions
Argument PromotionMethods(I) 2 3. Introdcution Most computer
programs that solve real-worldproblems are much larger than
programs thatyou have written yet! Experience has shown that the
best way todevelop and maintain a large program is toconstruct it
from small, simple pieces, ormodules. Methods are the building
blocks of C# and theplace 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 byseparating its tasks into self-contained
unitso Statements in method bodies are written only once Reused
from perhaps several locations in a program Hidden from other
methods Avoid repeating codeo Enable the divide-and-conquer
approacho Reusable in other programso User-defined or
programmer-defined methodsMethods(I) 4 5. Software engineering
tipTo promote software reusability, every methodshould be limited
to performing a single, well-definedtask, and the name of the
method shouldexpress that task effectively. Such methods
makeprograms easier to write, test, debug andmaintain.A small
method that performs one task is easierto test and debug than a
larger method thatperforms many tasks.Methods(I) 5 6. Methods in C#
C# programs are written by combining newmethods and classes
available in the .NET Framework Class Library(FCL) The FCL
provides: mathematical calculations, stringmanipulations, 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 callo Called method either
returns a result or simply returns to thecallero method calls form
hierarchical relationshipsMethods(I) 7 8. Math Class
MethodsMethods(I) 8 9. Math Class Methods (I) Math class methods
allow the programmer toperform certain common
mathematicalcalculations. Methods are called by writing the name of
themethod, followed by a left parenthesis, theargument and a right
parenthesis. The parentheses may be empty, if we are callinga
method that needs no information to performits task.Return a double
value Example: double x = Math.Sqrt( 900.0 )Methods(I) 9Argument
10. Software Engineering Observation 6.3 It is not necessary to add
an assemblyreference to use the Math class methodsin a program.
Class Math is located innamespace System, which is availableto
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 DefinitionsMethods(I) 14 15. Method Definitions (I) The
general form of a function isret-type method-name(parameter
list){body of the function} The ret-type specifies the type of data
that the methodreturns. A method may return any type of data except
an array. The parameter list is a comma-separated list of
variablenames and their associated types that receive the valuesof
the arguments when the function is called. Methods must be declared
within a class or astructure.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 followingsyntax (()) The method body is simply a C#
codeenclosed between { }Methods(I) 17 18. Method ExampleMethods(I)
18double computeTax(double income){double taxes ;if (income <
5000.0)return 0.0;taxes = 0.07 * (income-5000.0);return
taxes;}Function headerFunction body 19. Method Definitions (IV)
Basic characteristics of methods are: Return value typeo output:
data type or void Method nameo 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 parameterso inputs for the methodo Empty
parentheses indicate that the method requires no parameters.
Parentheses Block of statementso The method block is surrounded
with { } characters. Access levelo who can call the
methodMethods(I)
19ExecuteFindIdSetNameGetNameCheckIfValidTestValidity 20. Method
Signature The method signature is actually similar tothe method
header except in two aspects: The parameters names may not be
specifiedin the function signature The method signature must be
ended by asemicolon Example UnnamedParameterSemicolon;double
computeTaxes(double) ;double computeTaxes(double income)
;Methods(I) 20 21. Methods must be declared inside classInside
class every method should bepublic or private (later)This method
return nothing (void)Define an object for calling the
methodMethods(I) 21Calling the method 22. Method Definitions (V)
Each method must be defined inside a class or astruct. It must have
a name. In our case the name isShowInfo. The keywords that precede
the name of themethod are access specifier (public) and thereturn
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)
23static void Main(){...}This is the Main() method. It is the entry
point to each console or GUIapplication. 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 defaultone is used, which is private. 24.
Method Definitions (VII) We create an instance of the Base class.
We call the ShowInfo() method upon theobject. The method is called
by specifying theobject instance, followed by the memberaccess
operator the dot, followed by themethod name.Methods(I) 24Base bs =
new Base();bs.ShowInfo(); 25. Another ExampleMethods(I) 25 26.
Example: Tax computeA method to compute taxReturn type: doubleAn
input parameter (argument) : doubleMethods(I) 26 27. Example: Tax
computeA method to get salaryReturn type: doubleAn input parameter
(argument) : stringMethods(I) 27 28. Example: Tax computeA method
to print taxReturn type: voidAn input parameter (argument) :
doubleMethods(I) 28 29. Example: Tax computeDefine an object from
class: obob.NameofMethodCalling the methodsMethods(I) 29 30. More
about Method parametersMethods(I) 30 31. Method Parameters A
parameter is a value passed to themethod. Methods can take one or
moreparameters. If methods work with data, we must passthe data to
the methods. We do it by specifying them inside theparentheses. In
the method definition, we must providea name and type for each
parameter.Methods(I) 31 32. Example: Method parameters (I)Methods
should be inside a classMethods(I) 32 33. Example: Method
parameters (II)Method AddTwoValuesReturn type: intuse the return
keyword to return avalueInput parameters: int a, int bMethods(I) 33
34. Example: Method parameters (III)Method AddThreeValuesReturn
type: intuse the return keyword to return avalueInput parameters:
int a, int b, int cMethods(I) 34 35. Example: Method parameters
(IV)Define an object from class to callmethodsCalling methodsTwo
methods return integer, so x andy should be integersMethods(I) 35
36. Methods inside the Main class (I) Another Example: define
methods insidethe main classMethods(I) 36For methods inside the
main classAccess specifier: should be static 37. Methods inside the
Main class (II) Another Example: define methods insidethe main
classNo need to define an object. Directlyuse the name of method to
call themethodMethods(I) 37 38. Methods in Windows Application
FormsMethods(I) 38 39. Methods(I) 39 40. Methods(I) 40 41. Common
Programming Error 6.2 Defining a method outside the braces of
aclass definition is a syntax error.Methods(I) 41 42. Common
Programming Error 6.3 Omitting the return-value-type in a
methoddefinition is a syntax error. If a methoddoes not return a
value, the methodsreturn-value-type must be void.Methods(I) 42 43.
Common Programming Error 6.4 Forgetting to return a value from a
methodthat is supposed to return a value is asyntax error. If a
return-value-type otherthan void is specified, the method
mustcontain a return statement that returns avalue.Methods(I) 43
44. Common Programming Error 6.5 Returning a value from a method
whosereturn type has been declared void is asyntax errorMethods(I)
44 45. Common Programming Error 6.6 Placing a semicolon after the
rightparenthesis enclosing the parameter list ofa method definition
is a syntax error.Methods(I) 45 46. Common Programming Error 6.7
Redefining a method parameter in themethods body is a syntax
error.Methods(I) 46 47. Common Programming Error 6.9 Passing to a
method an argument that isnot compatible with the
correspondingparameters type is a syntax error.Methods(I) 47 48.
Common Programming Error 6.9 Defining a method inside another
methodis a syntax error (i.e., methods cannot benested)Methods(I)
48 49. Example: write a method to find maximumof three double
values Use windows application formMethods(I) 49 50. Methods(I) 50
51. Methods(I) 51 52. Methods(I) 52
