Master C# Programming From Scratch

Strings in C#

A string is a sequence of characters used to store and manipulate text. Strings are one of the most commonly used data types in C# and .NET applications.

Creating a String

In C#, the string keyword is used to declare a string variable. String values are written inside double quotation marks.

using System;
 
string name = "Rahul";

Console.WriteLine(name);

Output

Rahul

String Declaration

A string can first be declared and then assigned a value.

using System;
 
string firstName;

firstName = "Amit";

Console.WriteLine(firstName);

Output

Amit

String Concatenation

String concatenation means joining two or more strings together. The + operator can be used for concatenation.

using System;
 
string firstName = "Rahul";
string lastName = "Patil";

string fullName = firstName + " " + lastName;

Console.WriteLine(fullName);

Output

Rahul Patil

String Interpolation

String interpolation provides a clean and readable way to insert variables into a string. It uses the $ symbol.

using System;
 
string name = "Sneha";
int age = 22;

Console.WriteLine($"My name is {name} and my age is {age}.");

Output

My name is Sneha and my age is 22.

Accessing Characters

Individual characters of a string can be accessed using an index. String indexing starts from 0.

using System;

class Program
{
    static void Main()
    {
        string name = "CIIT";

        Console.WriteLine("Character 1: " + name[0]);
        Console.WriteLine("Character 2: " + name[1]);
        Console.WriteLine("Character 3: " + name[2]);
        Console.WriteLine("Character 4: " + name[3]);
    }
}

Output

Character 1: C
Character 2: I
Character 3: I
Character 4: T

String Length

The Length property returns the total number of characters in a string.

using System;
 
string text = "Hello";

Console.WriteLine(text.Length);

Output

5

ToUpper()

The ToUpper() method converts all characters in a string to uppercase.

using System;
 
string text = "ciit training";

Console.WriteLine(text.ToUpper());

Output

CIIT TRAINING

ToLower()

The ToLower() method converts all characters in a string to lowercase.

using System;
 
string text = "CIIT TRAINING";

Console.WriteLine(text.ToLower());

Output

ciit training

Trim()

The Trim() method removes whitespace from the beginning and end of a string.

using System;
 
string name = "   Rahul   ";

Console.WriteLine(name.Trim());

Output

Rahul

Contains()

The Contains() method checks whether a specified value exists inside a string. It returns true or false.

using System;
string message = "Welcome to CIIT Training Institute";

Console.WriteLine(message.Contains("CIIT"));

Output

True

StartsWith()

The StartsWith() method checks whether a string starts with a specified value.

using System;
 
string name = "Rahul";

Console.WriteLine(name.StartsWith("Rah"));

Output

True

EndsWith()

The EndsWith() method checks whether a string ends with a specified value.

using System;
 
string email = "student@gmail.com";

Console.WriteLine(email.EndsWith(".com"));

Output

True

Replace()

The Replace() method replaces a specified value with another value.

using System;
 
string message = "Hello Java";

string result = message.Replace("Java", "C#");

Console.WriteLine(result);

Output

Hello C#

Substring()

The Substring() method extracts a portion of a string.

using System;
 
string text = "Hello World";

string result = text.Substring(0, 5);

Console.WriteLine(result);

Output

Hello

Split()

The Split() method divides a string into multiple parts based on a specified separator.

using System;
 
string data = "Java,C#,Python";

string[] languages = data.Split(',');

foreach (string language in languages)
{
    Console.WriteLine(language);
}

Output

Java
C#
Python

String Comparison

Strings can be compared using the == operator.

using System;
 
string username1 = "admin";
string username2 = "admin";

if (username1 == username2)
{
    Console.WriteLine("Both strings are same");
}
else
{
    Console.WriteLine("Strings are different");
}

Output

Both strings are same

String Immutability

Strings in C# are immutable. This means that once a string object is created, its value cannot be changed directly. String operations create a new string.

using System;
 
string text = "Hello";

text = text + " World";

Console.WriteLine(text);

Output

Hello World

Common String Methods

Example 🌍❤️

String operations are commonly used in login systems, registration forms, search functionality and data validation.

using System;
 
string email = "  student@gmail.com  ";

email = email.Trim();

if (email.EndsWith("@gmail.com"))
{   
    Console.WriteLine("Valid Gmail Address");
}
else
{
    Console.WriteLine("Invalid Email Address");
}

Output

Valid Gmail Address

Common String Mistakes

• Remember that string indexing starts from 0.
• Do not access an invalid string index.
• Use Trim() when unwanted spaces may affect validation.
• Use Contains() when checking whether specific text exists.
• Remember that strings are immutable.
• Use string interpolation for readable formatted text.

Interview Questions

1. What is a string in C#?

A string is a sequence of characters used to represent text.

2. Are strings mutable or immutable?

Strings are immutable in C#.

3. What is string interpolation?

String interpolation allows variables and expressions to be inserted directly into a string using the $ symbol.

4. What does the Length property return?

It returns the total number of characters in a string.

5. What is the difference between String and StringBuilder?

String is immutable, while StringBuilder is designed for efficient modification of strings when many changes are required.

Strings Summary

• Strings are used to store text.
• String indexing starts from 0.
• The Length property returns the number of characters.
• String concatenation joins multiple strings.
• String interpolation provides readable formatted strings.
• Common methods include Trim(), Contains(), Replace(), Split() and Substring().
• Strings are immutable in C#.
• Strings are widely used in real-world .NET applications.

Practice Questions

1. Create a string variable and print its value.
2. Find the length of a string.
3. Convert a string to uppercase and lowercase.
4. Remove unnecessary spaces using Trim().
5. Check whether a string contains a specific word.
6. Replace one word with another word.
7. Extract a portion of a string using Substring().
8. Split a comma-separated string into multiple values.
9. Check whether an email ends with ".com".
10. Reverse a string using a C# program.