Common string methods in C Sharp (C#)

Introduction

String methods help you work with text easily. They let you change, check, or find parts of words or sentences.

When you want to change all letters to uppercase or lowercase.

When you need to find if a word contains a certain letter or phrase.

When you want to cut out a part of a sentence.

When you want to join words together or split a sentence into words.

When you want to remove spaces at the start or end of a sentence.

Syntax

C Sharp (C#)

string.MethodName(arguments);

Replace MethodName with the name of the string method you want to use.

Most string methods return a new string or a value; they do not change the original string.

Examples

This changes all letters in text to uppercase and saves it in upper.

C Sharp (C#)

string text = "hello";
string upper = text.ToUpper();

This checks if text contains the word "hello" and stores true or false in hasHello.

C Sharp (C#)

string text = "hello world";
bool hasHello = text.Contains("hello");

This takes the first 5 letters from text and saves it in part.

C Sharp (C#)

string text = "hello world";
string part = text.Substring(0, 5);

This removes spaces from the start and end of text and saves the result in trimmed.

C Sharp (C#)

string text = "  hello  ";
string trimmed = text.Trim();

Sample Program

This program shows common string methods: changing case, checking content, trimming spaces, and getting a part of the string.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
        string greeting = "  Hello World!  ";

        string upper = greeting.ToUpper();
        string lower = greeting.ToLower();
        bool containsWorld = greeting.Contains("World");
        string trimmed = greeting.Trim();
        string sub = greeting.Substring(2, 5);

        Console.WriteLine(upper);
        Console.WriteLine(lower);
        Console.WriteLine(containsWorld);
        Console.WriteLine(trimmed);
        Console.WriteLine(sub);
    }
}

Important Notes

Strings in C# are immutable. Methods return new strings; they do not change the original.

Use Trim() to clean spaces, Contains() to check for text, and Substring() to get parts.

Summary

String methods help you work with text easily and safely.

Common methods include ToUpper(), ToLower(), Contains(), Trim(), and Substring().

Remember, these methods return new strings and do not change the original text.

Practice

1. Which C# string method returns a new string with all characters converted to uppercase?

easy

A. Substring()

B. Trim()

C. Contains()

D. ToUpper()

Solution

1. Step 1: Understand the purpose of ToUpper()

   The ToUpper() method converts all letters in a string to uppercase and returns a new string.

2. Step 2: Compare with other methods

   Trim() removes spaces, Contains() checks for substring presence, Substring() extracts part of the string.

3. Final Answer:

   ToUpper() -> Option D

4. Quick Check:

   Uppercase conversion = ToUpper() [OK]

Hint: Uppercase all letters? Use ToUpper() method [OK]

Common Mistakes:

• Confusing ToUpper() with ToLower()
• Using Trim() to change case
• Thinking Contains() changes text

2. Which of the following is the correct syntax to check if the string text contains the word "hello"?

easy

A. Contains(text, "hello")

B. text.Contains = "hello"

C. text.Contains("hello")

D. text.Has("hello")

Solution

1. Step 1: Recall the correct method call syntax

   In C#, to check if a string contains another, use the instance method with parentheses: text.Contains("hello").

2. Step 2: Identify incorrect syntax

   Assignments (=) or wrong method names like Has() are invalid for this check.

3. Final Answer:

   text.Contains("hello") -> Option C

4. Quick Check:

   Method call with parentheses = Contains() [OK]

Hint: Use text.Contains("word") with parentheses [OK]

Common Mistakes:

• Using assignment instead of method call
• Wrong method name like Has()
• Passing parameters incorrectly

3. What is the output of the following code?

string s = "  Hello World  ";
string result = s.Trim().Substring(0, 5);
Console.WriteLine(result);

medium

A. " Hel"

B. "Hello"

C. "Hello "

D. "Hello World"

Solution

1. Step 1: Apply Trim() method

   Trim() removes spaces at the start and end, so " Hello World " becomes "Hello World".

2. Step 2: Apply Substring(0, 5)

   Substring(0, 5) extracts characters from index 0 to 4, which is "Hello".

3. Final Answer:

   "Hello" -> Option B

4. Quick Check:

   Trim + Substring(0,5) = "Hello" [OK]

Hint: Trim removes spaces; Substring extracts exact part [OK]

Common Mistakes:

• Not trimming before substring
• Counting spaces in substring
• Confusing substring length

4. Identify the error in this code snippet:

string s = "Example";
if(s.Contains("ex"))
{
    Console.WriteLine("Found");
}

medium

A. Contains() is case-sensitive, so "ex" won't match "Ex"

B. Missing semicolon after if statement

C. Contains() method does not exist for strings

D. Console.WriteLine syntax is incorrect

Solution

1. Step 1: Check Contains() behavior

   Contains() is case-sensitive, so "ex" does not match "Ex" in "Example".

2. Step 2: Verify syntax correctness

   Semicolons and method calls are correct; no syntax errors present.

3. Final Answer:

   Contains() is case-sensitive, so "ex" won't match "Ex" -> Option A

4. Quick Check:

   Contains() case matters = true [OK]

Hint: Remember Contains() is case-sensitive by default [OK]

Common Mistakes:

• Assuming Contains() ignores case
• Looking for syntax errors that don't exist
• Confusing method availability

5. You want to extract the domain name from an email string email = "[e-mail]". Which code correctly extracts "example" using common string methods?

hard

A. string domain = email.Substring(email.IndexOf('@') + 1).Split('.')[0];

B. string domain = email.Trim().ToUpper();

C. string domain = email.Contains("@example");

D. string domain = email.Substring(0, email.IndexOf('.'));

Solution

1. Step 1: Find position after '@'

   email.IndexOf('@') finds the '@' position; adding 1 moves to start of domain.

2. Step 2: Extract substring from domain start and split by '.'

   Substring gets "example.com", then Split('.')[0] gets "example".

3. Step 3: Check other options

   B changes case, C returns bool, D extracts wrong part before '@'.

4. Final Answer:

   string domain = email.Substring(email.IndexOf('@') + 1).Split('.')[0]; -> Option A

5. Quick Check:

   Extract domain by substring + split = string domain = email.Substring(email.IndexOf('@') + 1).Split('.')[0]; [OK]

Hint: Use IndexOf('@') + Substring + Split('.') to get domain [OK]

Common Mistakes:

• Using Contains() instead of extracting
• Trimming or changing case wrongly
• Extracting before '@' instead of after