Write a program to reverse a string?
using System;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
string str = "Hello";
char[] revStr = new char[str.Length];
int j = 0;
//Reverse a string
for(int i=str.Length-1;i>=0;i--)
{
revStr[j++] = str[i];
}
Console.WriteLine("Reverse String: {0}", new String(revStr));
}
}
}
This is interview question which is asked in many interviews.
Let’s see what Singleton is.
Singleton is design pattern, which allow user to create singleton
instance of class.
public sealed class Singleton
{
public static Singleton singleton = null;
private Singleton(){}
public static Singleton GetSingletonInstance()
{
if (singleton == null)
{
return new Singleton();
}
else
{
return null;
}
}
}
Here Singleton is a class and
it is marked as sealed, so it should not be
Inherited by any other classes.
Constructor is private, so object of Singleton class cannot be
created outside of this Singleton class.
GetSingletoninstance is method which returns instance of class.
Singleton:
namespace ConsoleApp3
{
//Interface which will be implemented by Singleton class
public interface IInterface
{
public void SHow();
}
// Singleton class inherit this
MyClass
public class MyClass
{
public void Disp()
{
Console.WriteLine("Disp");
}
}
{
public static
Singleton singleton = null;
private Singleton(){}
public void Disp()
{
Console.WriteLine(“Disp”);
}
{
if (singleton == null)
{
return new Singleton();
}
else
{
return null;
}
}
public void
Go(Singleton singleton)
{
singleton.Disp();
}
}
Static Class:
See in below image, it is throwing error when I am trying to create instance
of static class MyClass.
This is interview question, which is asked in one of interview.
How you can allow to create only 3 object in C#.NET. It should throw error when user is trying to create more than 3 object.
Here is logic and program.
using System;
using
System.Linq;
using
System.Collections.Generic;
{
{
static int count =
1;
public Student()
{
if (count <= 3)
{
count = count + 1;
}
else
{
throw new
Exception("you cannot create more than 3 instances");
//count =
0;
}
}
public int
MyProperty2 { get; set; }
}
class Program
{
static void Main(string[] args)
{
Student student2 = new Student();
}
}
}
Throw and throw ex both are used to throw exception caught
in catch block.
Throw: It preserve the stack trace.
Example: Method1
throw Error1 and caught by Method2 and again this method throws Error2
StackTrace:
Method1 Error1 + Method2Error2
 |
using System;
using
System.Collections.Generic;
{
class Program
{
static void Main(string[] args)
{
try
{
DevideNumberByZero(100);
}
catch (Exception ex)
{
throw;
}
}
{
try
{
Devide(num);
}
catch (Exception)
{
}
}
public static void Devide( int num)
{
try
{
int d = 0;
int res = num / d;
Console.WriteLine(res);
}
catch (Exception)
{
throw;
}
}
}
}
Output:
Throw Ex: It does not preserve stack trace, so it
will clear stack trace and will return only Method2Error2
Example: Method1 throw Error1 and caught by
Method2 and again this method throws Error2.
using System;
using System.Collections.Generic;
namespace ConsoleApp2
{
class Program
{
static void Main(string[] args)
{
try
{
DevideNumberByZero(100);
}
catch (Exception ex)
{
throw ex;
}
}
public static void DevideNumberByZero(int num)
{
try
{
Devide(num);
}
catch (Exception ex)
{
throw ex;
}
}
public static void Devide( int num)
{
try
{
int d = 0;
int res = num / d;
Console.WriteLine(res);
}
catch (Exception ex)
{
throw ex;
}
}
}
}
Output:
