Strings in C#

# CHAPTER 10

Strings in C# #

1. Introduction #

2. Learning Objectives #

• Use built-in String methods for text manipulation.

• Understand Escape Characters.

• Explain the concept of String Immutability.

• Use StringBuilder for high-performance string manipulation.

3. Built-in String Methods #

string text = "  Hello World!  ";

// 1. Length property
int len = text.Length; // 16

// 2. ToUpper() and ToLower()
string upper = text.ToUpper(); // "  HELLO WORLD!  "

// 3. Trim() - Removes leading and trailing whitespace
string cleanText = text.Trim(); // "Hello World!"

// 4. Contains() - Checks if text exists inside the string
bool hasWorld = cleanText.Contains("World"); // true

// 5. Replace()
string newText = cleanText.Replace("World", "C#"); // "Hello C#!"

// 6. Substring() - Extracts a portion of the string
string hello = cleanText.Substring(0, 5); // "Hello" (Starts at index 0, grabs 5 chars)

4. Escape Characters #

Verbatim Strings (@): Instead of using \\ for file paths, prefix the string with @ to ignore all escape characters.

string path = @"C:\Folder\File.txt"; // Much cleaner!

5. OOP and Memory: String Immutability (CRITICAL) #

string name = "John";
name = name + " Doe"; // What happens here?

When you add " Doe" to "John", C# does NOT modify "John". Instead, it:

1. 1. Creates a brand new block of memory for "John Doe".

1. 2. Changes the name variable to point to the new memory.

1. 3. Leaves the original "John" string in memory until the Garbage Collector deletes it.

If you concatenate strings in a for loop 10,000 times, you will create 10,000 abandoned strings in memory, causing massive lag!

6. The Solution: StringBuilder #

*(Requires using System.Text;)*

using System;
using System.Text;

namespace StringBuilderDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            // Creates a mutable string buffer
            StringBuilder sb = new StringBuilder();

            // Very fast! Does not create multiple strings in memory.
            for (int i = 0; i < 1000; i++) 
            {
                sb.Append("Word "); 
            }

            // Convert back to a standard string when finished
            string finalResult = sb.ToString();
        }
    }
}

7. Common Mistakes #

• Using == vs .Equals(): In Java, you must use .Equals() to compare strings. In C#, the == operator is heavily overloaded to compare the actual *value* of the strings safely. if(name == "Admin") is perfectly valid and preferred in C#.

• Ignoring Case Sensitivity: "apple" == "Apple" is false. Always use .ToLower() before comparing user input.

8. Best Practices #

• Use standard strings and the + operator (or interpolation $"") for simple concatenation (1-5 operations).

• Always use StringBuilder if you are modifying a string inside a loop.

9. Exercises #

1. 1. Write a program that asks for a user's full name, and prints their initials using Substring().

1. 2. Given the string "C:\Users\Admin\Desktop", print it to the console using a verbatim string literal (@).

10. MCQs with Answers #

11. Interview Questions #

• Q: Explain String Immutability and why it exists.

• Q: Describe the exact scenario where you would choose StringBuilder over standard string concatenation.

• Q: What happens in memory when you execute string s = "A"; s += "B"; s += "C";?

12. Summary #

13. Next Chapter Recommendation #