We will start with an introduction to what is object oriented programming, how to
write simple classes, creating objects etc.
What is a class�?
In modern object oriented programming, large computer programs are divided into
several 'classes'. Typically, a large project will have several hundred classes.
A class represents an entity in a program.
For example, if we are doing a small program called calculator, we will typically
have a single (or more) class called 'Calculator' .The class will have several
�methods� that will do the functionality of the class
So, our calculator may have methods like the following:
Add ()
Subtract ()
Multiply ()
Divide ()
Here is a sample calculator class, written in C# :
using System;
public class Calculator
{
public int Add(int value1, int value2)
{
return value1 + value2;
}
public int Subtract(int value1, int value2)
{
return value1 - value2;
}
public int Multiply(int value1, int value2)
{
return value1 * value2;
}
public int Divide(int value1, int value2)
{
return value1 / value2;
}
}
Methods
Any class in an object-oriented language has method and property members. These are
the places where the actual business logic or functionality is written and executed.
Method is object-oriented item of any language. All C# programs are constructed from
a number of classes and almost all the classes will contain methods. A class when
instantiated is called an object. Object-oriented concepts of programming say that
the data members of each object represent its state and methods represent the object
behavior.
Method Signature in C#:
Each method is declared as follows:
Return-type methodname ( Parameterslist );
For better understanding of methods let consider following example. We have a class Man.
It can have many fields like that:
public class Man
{
public Man(){}
private int m_old;
private string m_name;
public string WhatIsYourName()
{
Console.WriteLine(m_name);
return m_name;
}
public string HowOldAreYou()
{
Console.WriteLine(m_old.ToString());
return m_old;
}
}
The private members m_old and m_name define some state of objects that can be created
as instances of our class. Also the class Man has two methods, which serve some of our
requests. Method string WhatIsYourName() writes current object?s name to the console
and returns it, and the second one similar to first return age of man and also writes
an output to the console
The return type in the example above returns strings, which is an in-built data type.
The methods can also return any generic C# type or any custom types created by us.
Passing Parameters to Methods in C#:
The input parameters can be passed in two ways.
Value type
Reference type
Output Parameters in Methods:
The return values in any function will be enough for any one if only one value is
needed. But in case a function is required to return more than one value, then
output parameters are the norm. This is not supported in C++ though it can be
achieved by using some programming tricks. In C# the output parameter is declared
with the keyword out before the data type. A typical example is as follows.
public void CalculateBirthYear(ref int year, out int birthyear)
{
int b = year - m_old;
Console.WriteLine("Birth year is {0}",b);
birthyear = b;
return;
}
Strictly speaking there is no difference between ref and out parameters. The only
difference is that the ref input parameters need an input value and the out parameters
don?t.
Variable arguments in C#:
The C# language supports variable arguments through a keyword called params. A typical
example for the declaration of a function with variable argument signature is as
follows.
Public void functionName(int a, params int[] varParam);
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