Post
Ask Question

Test Your C# Skills - Part One

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?   
  1.        public static void Main()  
  2.        {  
  3.            Console.writeLine("Welcome");  
  4.            Console.ReadKey();  
  5.        }  
Answer

'Console' does not contain a definition for 'writeLine'
  1. public static void Main()  
  2.         {  
  3.             Console.WriteLine("Welcome");  
  4.             Console.ReadKey();  
  5.         }  
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?
  1. public static void Main(string[] args)  
  2.         {  
  3.             Console.WriteLine("Hi")  
  4.             Console.ReadKey();  
  5.         }  
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.
  1. public static void Main(string[] arg)  
  2.         {  
  3.             Console.WriteLine("Hi");  
  4.             Console.ReadKey();  
  5.         }  
What Is the output of the below code snippet?
  1. public static void Main(string[] arg)  
  2.        {  
  3.            string a = "Hi , I am {0} {1}";  
  4.            string b = "software";  
  5.            string c = "engineer";  
  6.            Console.WriteLine(a,b,c);  
  7.            Console.ReadKey();  
  8.        }  
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 
  1. Console.WriteLine(a,b,c);  
  2. Console.WriteLine("Hi , I am {0} {1}","software","engineer"); // {0}=software and {1} =engineer  
  3. Console.WriteLine("Hi , I am software engineer");  
What Is the output of the below code snippet?
  1. public static void Main(string[] args)  
  2.         {  
  3.             string a = "{0} should be greater than {1} and less than {2}";  
  4.             string Age = "Age";  
  5.             int minAge = 1;  
  6.             int maxAge = 99;  
  7.             Console.WriteLine(a,Age,minAge,maxAge);  
  8.             Console.ReadKey();  
  9.         }  
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?
  1. public static void Main(string[] args)  
  2.         {  
  3.             short a = 45;  
  4.             short b = 26;  
  5.             int c;  
  6.             c = a * b;  
  7.             Console.WriteLine(c);  
  8.             Console.ReadKey();  
  9.         }  
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?
  1. public static void Main(string[] args)  
  2. {  
  3.     int c = 25;  
  4.     Console.WriteLine("1st {0}",c);  
  5.     Console.WriteLine("2nd {0}",c++);  
  6.     Console.WriteLine("3rd {0}",c);  
  7.     c--;  
  8.     Console.WriteLine("4th {0}",c);  
  9.     Console.WriteLine("5th {0}",++c);  
  10.     Console.WriteLine("6th {0}",c);  
  11.     --c;  
  12.     Console.WriteLine("7th {0}",c);              
  13.     Console.ReadKey();  
  14. }  
Answer

1st 25
2nd 25
3rd 26
4th 25
5th 26
6th 26
7th 25
  1. public static void Main(string[] args)
  2. {
  3. int c = 25;
  4. Console.WriteLine("1st {0}",c);
  5. Console.WriteLine("2nd {0}",c++);     // c increment by 1 after printing.  it's clalled Post increment
  6. Console.WriteLine("3rd {0}",c);
  7. c--;
  8. Console.WriteLine("4th {0}",c);
  9. Console.WriteLine("5th {0}",++c);    // first increment c and then then print  1
  10. Console.WriteLine("6th {0}",c);
  11. --c;
  12. Console.WriteLine("7th {0}",c);
  13. Console.ReadKey();
  14. }
 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
  1. public static void Main(string[] args)  
  2. {  
  3.     int fnum = 10, snum = 20;  
  4.     fnum = fnum + snum;  
  5.     snum = fnum - snum;  
  6.     fnum = fnum - snum;  
  7.     Console.WriteLine("First Number is {0}\n Second Number is {1}",fnum,snum);  
  8.     Console.ReadKey();  
  9. }  
Output is:

First Number is 20
Second Number is 10
 
What is the output of the below code snippet?
  1. public static void Main(string[] args)  
  2. {  
  3.     int a = 6;  
  4.     int b = 9;  
  5.     int c;  
  6.     Console.WriteLine(++a + b++);  
  7.     Console.ReadKey();  
  8. }  
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?
  1. public static void Main(string[] args)  
  2.         {  
  3.             float a = 5.5;  
  4.             decimal b = 1000.5;  
  5.             Console.ReadKey();  
  6.         }  
Answer - there are two errors.
  1. Use f suffix in float data type 
  2. Use m suffix in decimal data type  
  1. public static void Main(string[] args)  
  2. {  
  3.     float a = 5.5f;  
  4.     decimal b = 1000.5m;  
  5.     Console.ReadKey();  
  6. }  
What Is the output of the below code snippet?
  1. public static void Main(string[] args)  
  2. {  
  3.     string str = "I am human bein";  
  4.     char c = 'g';  
  5.     Console.WriteLine(str+c);  
  6.     Console.ReadKey();  
  7. }  
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? 
  1. public static void Main(string[] args)  
  2. {  
  3.     int a = 10;  
  4.     int b = 20;  
  5.     Console.WriteLine(a<b);  
  6.     Console.ReadKey();  
  7. }  
Answer
TRUE
 
WriteLine has several overloaded methods:
  1. public static void WriteLine(bool value);  
  2. public static void WriteLine(float value);  
  3. public static void WriteLine(int value);  
  4. public static void WriteLine(uint value);  
  5. 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?
  1. public static void Main(string[] args)  
  2. {  
  3.    const int a = 10;  
  4.     int b = 20;  
  5.     const int  c= 100 * b;  
  6.     Console.WriteLine(c);  
  7.     Console.ReadKey();  
  8. }  
 Answer

Compile time Error: The expression being assigned to 'c' must be constant. 
 
What Is the output of the below code snippet?
  1. public static void Main(string[] args)  
  2. {  
  3.     string s = "Ankit";  
  4.     s = s.Insert(5, "Sahu");  
  5.     Console.WriteLine(s);  
  6.     Console.ReadKey();  
  7. }  
 Answer

AnkitSahu
 
Insert method is just inserting the value based on an index
 
What Is the output of the below code snippet? 
  1. public static void Main(string[] args)  
  2.         {  
  3.             string s = "Ankit";             
  4.             Console.WriteLine(s.IndexOf("k"));  
  5.             Console.ReadKey();  
  6.         }  
 Answer

2      
A  N  K   I   T
0   1   2    3    4     
 
What Is the output of the below code snippet?
  1. public static void Main(string[] args)  
  2. {          
  3.     Console.WriteLine(Convert.ToInt32((30 > 20)));  
  4.     Console.WriteLine(Convert.ToDouble((30 < 20)));  
  5.     Console.WriteLine(Convert.ToSingle((30 > 20)));  
  6.     Console.ReadKey();  
  7. }  
Answer

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

Output is: 
1
0
1
 
What is the output of the below code snippet?
  1. public static void Main(string[] args)  
  2.         {  
  3.             string s = "Hello"+"?";  
  4.             Console.WriteLine(string.Compare(s, "Hello?").GetType());  
  5.             Console.ReadKey();  
  6.         }  
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! !!!
Next Recommended Reading How To Create An Excel File (Development) Using EPPlus .NET Library (C#) - Part One