Visual C Sharp Methods and Classes 1

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Visual C Sharp Methods and Classes 1

• Modular code
• Break program into small defined routines
• Each with a defined and testable function
• Easier to debug - re-usable
• Called a Method
• e.g. Button_click
• AKA function, procedure or subroutine
• Classes are part of Object oriented code
• Combined method and data
• e.g. We have seen the Math class and methods
  (Cos)
• And DateTime class, methods Now, AddHours
• (remember naming convention Upper case)

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Visual C Sharp Methods and Classes 2

• The Math class
• Does common math calculations
• Use ClassName.MethodName (param 1, param2 )
• e.g. Math.Sin(x), Math.Exp(y)
• Also constants
• Math.PI 3.1415926535
• Math.E 2.7182818285
• Use dot notation

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Visual C Sharp Methods and Classes 3

• Method declaration
• Return data type (or void if none)
• Name
• Parameters
• ltdata typegt ltnamegt ltparametersgt
• Example Square root return double, pass
  integer
• double SquareRoot ( int sq )
• // code goes here
• Called using its name
• double SqRoot SquareRoot(3)

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Visual C Sharp Methods and Classes 4

• Code
• double SquareRoot ( int sq )
• return Math.Sqrt(sq) //Math.Sqrt returns a
  double
• private void button1_Click(object sender,
  EventArgs e)
• double SqRoot SquareRoot(3)
• MessageBox.Show(SqRoot.ToString())
• Display 1.73205080756888
• Note button click is method too!

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Visual C Sharp Methods and Classes 5

• Suppose we only wanted float precision?
• How do we override Math.Sqrt double return value?
• Use explicit (float)
• float SquareRoot ( int sq )
• return (float)Math.Sqrt(sq)
• Call using float SqRoot SquareRoot(3)
• Display 1.732051

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Visual C Sharp Methods and Classes 6

• Reserved word return used to return value
• sq used in method may be another name in
  calling routine
• int two 2
• int three 3
• int root2 SqRoot(two)
• int root3 SqRoot(three)

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Visual C Sharp Methods and Classes 7

• Method use
• Nothing returned? - use void
• Nothing passed? - empty brackets
• Four cases
• Pass nothing, return nothing,
• Pass something, return nothing,
• Pass nothing, return something,
• Pass something, return something.
• void delay( )
• void delay(int delayTime)
• boolean done( ) // return true when done
• double SqRoot(int sq) // already seen

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Visual C Sharp Methods and Classes 8

• Example 1 A delay Wait pass/return nothing
• void Wait( )
• int i 0
• while (i lt 10) i i 1
• Call using
• private void button1_Click(object sender,
  EventArgs e)
• Wait( )

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Visual C Sharp Methods and Classes 9

• Example 2a Pass delay time, return nothing
• void PassWaitTime(int delayTime)
• int i 0
• while (i lt delayTime) i i 1
• Call using
• private void button1_Click(object sender,
  EventArgs e)
• PassWaitTime(10)

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Visual C Sharp Methods and Classes 10

• Example 2b - Can pass variable
• int longTime 10000
• int shortTime 10
• Wait(longTime)
• Wait(shortTime)
• Note variable name is longTime or shortTime in
  main program, but delayTime in method.
• Can we declare delayTime in main program?
• Yes but is a different version variable
  scope

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Visual C Sharp Methods and Classes 11

• Example 3 Pass nothing, return something
• Wait routine returns string done
• string ReturnWait( )
• int i 0
• while (i lt 10) i i 1
• return done
• Have do to something with returned value
• private void button1_Click(object sender,
  EventArgs e)
• MessageBox.Show(ReturnWait( ))

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Visual C Sharp Methods and Classes 12

• Example 4 Pass and return value
• string PassReturnWait(int delayTime)
• int i 0
• while (i lt delayTime) i i 1
• return done
• Call
• int shortTime 10
• MessageBox.Show(ReturnWait( shortTime))

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Visual C Sharp Methods and Classes 13

• Variables
• Declared in a method local variables
• Declared outside a method global variables
• AKA scope where it can be referenced in the
  program
• Only the method that defines them know they exist
• Send parameters to communicate with other methods

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Visual C Sharp Methods and Classes 14

• What if we want to pass or return more values?
• Add to parameter list, example button click
• private void button1_Click(object sender,
  EventArgs e)
• Note passing an object and event details here
• What if we want to pass hundreds of items?
• Pass pointer to array or structure
• Pass by value. Copy made seen this
• Pass by reference. Address of variable passed
• faster but insecure
• Keywords ref and out

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Visual C Sharp Methods and Classes 15

• Methods can call themselves - Recursive
• Breaks problem down to simpler forms
• Must be a way out!
• Example Factorial
• N! N(N-1)! N(N-1)(N-2)!
• 1! 1

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Visual C Sharp Methods and Classes 16
Final value 120
5! 5 24 120 is returned
4! 4 6 24 is returned
3! 3 2 6 is returned
2! 2 1 2 is returned
1 returned
(b) Values returned from each recursive call.
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Visual C Sharp Methods and Classes 17

• int Factorial(int factorialNo)
• if (factorialNo 0)
• return 1
• else
• return factorialNo Factorial(factorialNo
  - 1)
• Call
• int fac5 Factorial(5) // soon gets a large
  number !

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Visual C Sharp Methods and Classes 18

• Method overloading
• Methods can have the same name but different
  number (or type) of arguments
• Usually perform the same task on different data
  types
• Example
• MessageBox.Show(text )
• MessageBox.Show("text,"caption")
• MessageBox.Show(text", caption, buttons,
  icon)
• See how to do this later

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Visual C Sharp Methods and Classes 19

• Classes and Objects
• Consider a button object
• Each button has its own data (properties) and
  methods (buttonClick)
• All created from same code (method and data) a
  class
• A class is a method with its own data (e.g.
  .top)
• An object is a unique case (called an instance)
  of a class
• How do we define a class? - Later

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Visual C Sharp Methods and Classes 20

• Suppose we want our method to have its own
  methods?
• No problem
• BUT do we want it to be seen by main program?
• Private, public, protected methods
• Private local to method/class
• Public seen everywhere
• Protected intermediate accessed by class or
  classes derived from it - OOP

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Visual C Sharp Methods and Classes 21

• Namespace
• A group of classes and their methods
• .NET library (FCL) is composed of namespaces
• Namespaces are stored in .dll files called
  assemblies
• Some FLC namespaces
• System, System.IO, System.Windows.Forms
• Included in a program with the using keyword

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Visual C Sharp Methods and Classes 22

• Summary
• Methods break up program
• Reusable
• Declare return and passed variables and types
• Pass data to and from methods.
• OOP
• Classes combine data (properties) and code
  (method)
• Objects individual case (instance) of a class