Test Your C# Skills

Introduction

In this blog, I will discuss some C# coding interview questions which every developer should know. All questions contain a unique coding snippet.

Try to attempt each question carefully and test your C# programming skills. Solving these coding questions should be fun for you.

Also, I’ve listed down some quick C# coding tips which could be quite handy while programming.

C# Basic Question

What Is the error of the below code snippet?

public static void Main()
{
Console.writeLine("Welcome");
Console.ReadKey();
}

Answer

'Console' does not contain a definition for 'writeLine'

public static void Main()
{
Console.WriteLine("Welcome");
Console.ReadKey();
}

Note

C# is a case sensitive language so if you change case it is treated as a different method or variable and Console. WriteLine is present in System namespace in C# where a console is a static class and WriteLine is a method.

Use of Console.WriteLine

There are two console methods to render the text in a console application.

Console.Write
Console.WriteLine

Console.Write

The use of Console.Write to render text in a console application.

e.g.:

Console.Write("Hello world");

Console.WriteLine

The use of Console.Write to render text with a line break in a console application.

e.g.:

Console.WriteLine("Hello world");

What is an error in the following set of code?

public static void Main(string[] args)
{
Console.WriteLine("Hi")
Console.ReadKey();
}

Answer

All CSharp statements terminate with a semicolon ( ; ) if you miss it the compiler will give you an "Console.WriteLine("Hi") semicolon expected." error. You can write a single or multiple statements on a single line but all statements end with the semicolon. A semicolon is mandatory.

public static void Main(string[] arg)
{
Console.WriteLine("Hi");
Console.ReadKey();
}

What Is the output of the below code snippet?

public static void Main(string[] arg)
{
string a = "Hi , I am {0} {1}";
string b = "software";
string c = "engineer";
Console.WriteLine(a,b,c);
Console.ReadKey();
}

Answer

Hi, I am a software engineer.

Note

In C# {0},{1} is called a placeholder syntax. The main use of placeholder syntax is for string concatenation. In runtime {0} replace with the value b (software) and {1} replace with the value c (engineer).

e.g

Console.WriteLine(a,b,c);
Console.WriteLine("Hi , I am {0} {1}","software","engineer"); // {0}=software and {1} =engineer
Console.WriteLine("Hi , I am software engineer");

What Is the output of the below code snippet?

public static void Main(string[] args)
{
string a = "{0} should be greater than {1} and less than {2}";
string Age = "Age";
int minAge = 1;
int maxAge = 99;
Console.WriteLine(a,Age,minAge,maxAge);
Console.ReadKey();
}

Answer

Age should be greater than 1 and less than 99.

Note

{0} should be greater than {1} and less than {2}

here {0} replace with Age

{1} replace with 1

{2} replace with 99

So, the final output is "Age should be greater than 1 and less than 99"

Data Types Question

What Is the output of the below code snippet?

public static void Main(string[] args)
{
short a = 45;
short b = 26;
int c;
c = a * b;
Console.WriteLine(c);
Console.ReadKey();
}

Answer

c=45*26= 1170 so the answer is 1170

Note

Short and int both are integers; short contains only 16 bits but int contains 32 bits -- just double the memory --- that's why integer accepts short (no data loss) but short can't accept int (memory loss) so, if you want to assign int to short; you should use convert function in C#.

What is the output of the below code snippet?

public static void Main(string[] args)
{
int c = 25;
Console.WriteLine("1st {0}",c);
Console.WriteLine("2nd {0}",c++);
Console.WriteLine("3rd {0}",c);
c--;
Console.WriteLine("4th {0}",c);
Console.WriteLine("5th {0}",++c);
Console.WriteLine("6th {0}",c);
--c;
Console.WriteLine("7th {0}",c);
Console.ReadKey();
}

Answer

1st 25

2nd 25

3rd 26

4th 25

5th 26

6th 26

7th 25

public static void Main(string[] args)
{
int c = 25;
Console.WriteLine("1st {0}",c);
Console.WriteLine("2nd {0}",c++); // c increment by 1 after printing. it's clalled Post increment
Console.WriteLine("3rd {0}",c);
c--;
Console.WriteLine("4th {0}",c);
Console.WriteLine("5th {0}",++c); // first increment c and then then print 1
Console.WriteLine("6th {0}",c);
--c;
Console.WriteLine("7th {0}",c);
Console.ReadKey();
}

Note

There are two ways to increase the value of C#

Pre-Increment
Post-Increment

Pre-Increment: first increment value +1 then print (++Value)

Post-Increment: print first then increment value +1 (Value++)

Swap two numbers without using the third variable in C#

Answer

public static void Main(string[] args)
{
int fnum = 10, snum = 20;
fnum = fnum + snum;
snum = fnum - snum;
fnum = fnum - snum;
Console.WriteLine("First Number is {0}\n Second Number is {1}",fnum,snum);
Console.ReadKey();
}

Output is:

First Number is 20

Second Number is 10

What is the output of the below code snippet?

public static void Main(string[] args)
{
int a = 6;
int b = 9;
int c;
Console.WriteLine(++a + b++);
Console.ReadKey();
}

Answer

7+9=16

Note

++a in pre-increment value; first increase value by 1 and then calculate.

b++ in post-increment value; first print or use your value and later increase by 1.

What is the error in the below code?

public static void Main(string[] args)
{
float a = 5.5;
decimal b = 1000.5;
Console.ReadKey();
}

Answer - there are two errors.

Use f suffix in float data type
Use m suffix in decimal data type

public static void Main(string[] args)
{
float a = 5.5f;
decimal b = 1000.5m;
Console.ReadKey();
}

What Is the output of the below code snippet?

public static void Main(string[] args)
{
string str = "I am human bein";
char c = 'g';
Console.WriteLine(str+c);
Console.ReadKey();
}

Answer - I am a human being

Note

Console.WriteLine(str+c) worked as cancellation

e.g.: "I am a human bein"+"g" = "I am a human being"

What Is the output of the below code snippet?

public static void Main(string[] args)
{
int a = 10;
int b = 20;
Console.WriteLine(a<b);
Console.ReadKey();
}

Answer

TRUE

WriteLine has several overloaded methods:

public static void WriteLine(bool value);
public static void WriteLine(float value);
public static void WriteLine(int value);
public static void WriteLine(uint value);
public static void WriteLine(long value);

So, if you passed a bool condition into a writeline method it will work as a boolean value in the console application.

What is the error in the below code?

public static void Main(string[] args)
{
const int a = 10;
int b = 20;
const int c= 100 * b;
Console.WriteLine(c);
Console.ReadKey();
}

Answer

Compile time Error: The expression being assigned to 'c' must be constant.

What Is the output of the below code snippet?

public static void Main(string[] args)
{
string s = "Ankit";
s = s.Insert(5, "Sahu");
Console.WriteLine(s);
Console.ReadKey();
}

Answer

AnkitSahu

Insert method is just inserting the value based on an index

What Is the output of the below code snippet?

public static void Main(string[] args)
{
string s = "Ankit";
Console.WriteLine(s.IndexOf("k"));
Console.ReadKey();
}

Answer

2

A N K I T

0 1 2 3 4

What Is the output of the below code snippet?

public static void Main(string[] args)
{
Console.WriteLine(Convert.ToInt32((30 > 20)));
Console.WriteLine(Convert.ToDouble((30 < 20)));
Console.WriteLine(Convert.ToSingle((30 > 20)));
Console.ReadKey();
}

Answer

In this case, all functions behave as a boolean and it behaves as a boolean and returns 1 or 0

Output is:

What is the output of the below code snippet?

public static void Main(string[] args)
{
string s = "Hello"+"?";
Console.WriteLine(string.Compare(s, "Hello?").GetType());
Console.ReadKey();
}

Answer

System.Int32

string.Compare is used to compare a string value; if both are the same it will return true, otherwise false, and GetType will return data type like int, float, double etc.

I hope it is helpful to you. If you face any problems drop a comment or message to me.

Thank you for reading! !!!