ashish

Both are used for implementing polymorphism in c#.One is compile time polymorphism-Method overloading.Other is runtime polymorphism-method overriding.

Method Overloading

Here you define two methods in the same class with the same name but different signatures. In the following example Common class defines two method PrintName which are used for printing name of an employee.
First overload takes the name to print while the other overload takes the Employee object as parameter.

class Common
{
public void PrintName(string FullName)
{

Console.WriteLine(FullName);
}

public void Print(Employee emp)
{
Console.WriteLine(emp.FirstName+emp.LastName);
}

Now when you call the PrintName() method then the method to call is determined on the bases of the arguments you pass while calling the method.For example if you use the following method call:

PrintName("Steve")

then first version of the method will be called.

Method Overriding

You define two methods with the same signature,one in derived class and other in base class.In the following example we have declared two classes Manager and Employee.The Employee class defines a Details() method which does not have any parameters.This method just prints the name of the Employee.In the derived Manager class we have overridden this method to print the names of all the employees which a Manager manages.

class Manager: Employee
{
public List<Employee> Employees{get;set;}
public virtual void Details()
  {
  foreach(var emp in Employees)
        {
      Console.WriteLine(emp.Name);
    }
  }
}

class Manager: Employee
{
public string Name{get;set;}
public virtual void Details()
{
Console.WriteLine(Name);
}
}

In method overloading the method to call is determined at runtime,based on the reference used to call the method.If you call the following method then base class method will be called

Employee emp=new Employee();
emp.Details()

If you use the below method call then the derived class method will be called.

Employee mgr=new Manager();
mgr.Details()

 

Follow on:

Three types in System namespace are used for working with date and time values.People wrongly believe that DateTime is a class,all of these are structs.

Date time structs for working with date and time values:

• DateTime   Stores value as ticks and DateTimeKind enum for identifying date and time.
• DateTimeOffset Stores value as timestamp (called offset) from UTC.
• TimeSpan  Represents interval of time

DateTime struct

DateTime is the most commonly used type for working with date time values.It defines the following properties.All of these are get only,you can not modify after you create a DateTime value:

• Date
• Day
• Hour
• Minute
• Month
• Year
• Second

Creating DateTime object

Using constructors

You pass the values for day,month,year,hour,minute and second.Some of the constructors it provides are:

DateTime(int year, int month, int day);

DateTime(int year, int month, int day, int hour, int minute, int second);

public DateTime(int year, int month, int day, int hour, int minute, int second, int millisecond);

public DateTime(int year, int month, int day, int hour, int minute, int second, int millisecond, DateTimeKind kind);

public DateTime(int year, int month, int day, int hour, int minute, int second, int millisecond, Calendar calendar);

For example to create a date object for the year 2019,day 1 and month 9:

var dateObj = new DateTime(2019, 9, 1);

After you have created a datetime variable you can access its various properties,to get the appropriate value.

Adding DateTime values

To add datetime values you use the AddXXX methods.

At a minimum you need to specify at least day,month and year or tick.You specify day,month and year as int

Some of the common methods are:

AddDays(double value);
AddHours(double value);
AddMinutes(double value);
AddMilliseconds(double value);
AddMonths(int months);
AddYears(int value);

Examples

Adding days

You can add one day to a DateTime object as:

var dateObj = new DateTime(2019, 9, 1);
var newdateObj = dateObj.AddDays(1);

Substracting Days

Outputting DateTime

You can use ToString() method on any date time object to print its value.By default it prints the short datetime value.

var newdateObj = new DateTime(2019, 9, 2);

Console.WriteLine(newdateObj.ToString());

Output:

9/2/2019 12:00:00 AM

TimeSpan

You use TimeSpan to find the difference between two date time values.For example you can find the difference between the following beginning and stopDate as:

DateTime beginingDateTime = DateTime.Now;
DateTime stopDateTime = DateTime.Now.AddDays(1);
TimeSpan difference = stopDateTime - beginingDateTime;

 

Follow on: