String Methods — The Label Maker 15 XP Medium

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🏷️ The Architect's Label Maker

On every construction site, labels are everywhere — door signs, blueprint tags, safety notices, material codes. The architect needs a reliable label maker, and in .NET, the string class is exactly that: a rich, powerful toolkit for manipulating text.

In C#, string is an alias for System.String. Strings are immutable — every operation that appears to modify a string actually creates a new string object on the heap. This immutability makes strings thread-safe and enables an optimization called string interning, but it also means careless string manipulation can generate lots of garbage for the GC to collect.

🔤 Case Conversion

Converting text to uppercase or lowercase is a daily task for the label maker — project names go on official signage in uppercase, while internal logs use lowercase.

string project = "Skyline Tower";

Console.WriteLine(project.ToUpper());   // SKYLINE TOWER
Console.WriteLine(project.ToLower());   // skyline tower

// Culture-aware versions for international projects
Console.WriteLine(project.ToUpperInvariant()); // SKYLINE TOWER
Console.WriteLine(project.ToLowerInvariant()); // skyline tower

✂️ Substring and Indexing

Substring extracts a portion of the string. IndexOf finds where a character or substring first appears. Together, they're like a precision cutting tool for labels.

string code = "PROJ-SKY-2024-TOWER";

// Substring(startIndex) — from index to end
Console.WriteLine(code.Substring(5));       // SKY-2024-TOWER

// Substring(startIndex, length) — extract exact portion
Console.WriteLine(code.Substring(5, 3));    // SKY

// IndexOf — find position
Console.WriteLine(code.IndexOf("2024"));    // 9
Console.WriteLine(code.IndexOf('T'));       // 14

// LastIndexOf — find last occurrence
Console.WriteLine(code.LastIndexOf('-'));    // 13

🔄 Replace, Trim, and Contains

These methods handle cleanup and verification — essential when processing messy input from site reports.

string input = "   Steel, Wood, Glass   ";

// Trim — remove leading/trailing whitespace
Console.WriteLine(input.Trim());        // "Steel, Wood, Glass"
Console.WriteLine(input.TrimStart());   // "Steel, Wood, Glass   "
Console.WriteLine(input.TrimEnd());     // "   Steel, Wood, Glass"

// Replace — swap characters or substrings
string updated = input.Trim().Replace("Wood", "Titanium");
Console.WriteLine(updated); // "Steel, Titanium, Glass"

// Contains, StartsWith, EndsWith — boolean checks
Console.WriteLine("Skyline Tower".Contains("Tower"));      // True
Console.WriteLine("Skyline Tower".StartsWith("Sky"));      // True
Console.WriteLine("Skyline Tower".EndsWith("er"));         // True

🔪 Split and Join — Disassemble and Reassemble

Split breaks a string into an array of substrings. Join fuses an array back into a single string. They're the architect's ability to take apart a label and put it back together in a new format.

string csv = "Steel,Wood,Glass,Concrete";

// Split on comma
string[] parts = csv.Split(',');
Console.WriteLine(parts.Length); // 4
Console.WriteLine(parts[2]);    // Glass

// Join with a different separator
string spaced = String.Join(" | ", parts);
Console.WriteLine(spaced); // Steel | Wood | Glass | Concrete

// Split with multiple delimiters
string messy = "Steel;Wood,Glass|Concrete";
string[] items = messy.Split(new char[] { ';', ',', '|' });
Console.WriteLine(items.Length); // 4

📝 String Interpolation and Formatting

Modern C# provides elegant ways to compose strings from variables and expressions.

string name = "Skyline Tower";
int year = 2024;

// String interpolation (C# 6+) — the preferred way
string label = $"Project: {name} ({year})";
Console.WriteLine(label); // Project: Skyline Tower (2024)

// Composite formatting with String.Format
string formatted = String.Format("Code: {0}-{1}", "SKY", year);
Console.WriteLine(formatted); // Code: SKY-2024

// Padding — great for aligned output
Console.WriteLine("Item".PadRight(15) + "Qty");
Console.WriteLine("Steel Beams".PadRight(15) + "42");
Console.WriteLine("Glass Panels".PadRight(15) + "88");

🔃 Reversing a String

C# doesn't have a built-in string.Reverse(), but you can convert to a char array, reverse it, and create a new string:

string name = "Skyline Tower";

char[] chars = name.ToCharArray();
Array.Reverse(chars);
string reversed = new string(chars);
Console.WriteLine(reversed); // rewoT enilykS

⚡ Key Takeaways

Strings are immutable — every modification creates a new string object.
ToUpper() / ToLower() for case conversion; use Invariant versions for culture-independent comparisons.
Substring(), IndexOf(), and LastIndexOf() for extracting and locating parts of a string.
Split() turns a string into an array; String.Join() turns an array back into a string.
Use $"..." string interpolation for readable string composition.
PadLeft() / PadRight() for aligned, fixed-width output.
Reverse a string by converting to char[], calling Array.Reverse(), then new string(chars).

📋 Instructions

## 🏷️ Architect's Label Maker Challenge The architect needs a set of labels for project **Skyline Tower**. Build the label maker! 1. Create a `string` variable `project` with value `"Skyline Tower"` 2. Print the project in UPPERCASE: `"PROJECT: SKYLINE TOWER"` 3. Print the project in lowercase: `"project: skyline tower"` 4. Create a project code by taking the first 3 characters of `project`, converting to uppercase, and combining with `"-2024"`. Print: `"Code: SKY-2024"` 5. Split `project` by `' '` (space) and print the word count: `"Words: 2"` 6. Reverse the string `project` and print: `"Reversed: rewoT enilykS"`

Use `project.ToUpper()` and `project.ToLower()` for case conversion. For the code, use `project.Substring(0, 3).ToUpper() + "-2024"`. Split with `project.Split(' ')` and check `.Length`. To reverse, convert to `char[]` with `ToCharArray()`, call `Array.Reverse()`, then `new string(chars)`.

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