C# Strings & Text — Hands-on Examples

Part 09 of a hands-on C# practice series. Five runnable, heavily commented examples: immutability and interning proven with ReferenceEquals, the +=-in-a-loop disaster measured against StringBuilder, culture formatting traps (the "3,50" → 350 silent corruption, date ambiguity), correct comparing (StringComparison, the Turkish-i bug reproduced live), and regex essentials with [GeneratedRegex] and ReDoS timeouts.

Running

dotnet run        # all examples
dotnet run 3      # just one (e.g. culture traps)

What's inside

#	Topic	Highlights
01	Immutability	methods return new strings, interning, why == compares content
02	StringBuilder	20k appends measured, the API tour, when plain strings win
03	Formatting & culture	specifiers, alignment, "3,50" parsed as 350 in en-US, ISO dates
04	Comparing	StringComparison everywhere, Turkish-i reproduced, ordinal vs culture sort
05	Regex	[GeneratedRegex], named groups, MatchEvaluator, ReDoS timeout demo

The rules to remember

1. Machines get InvariantCulture; humans get their own culture — never the ambient default.
2. Every Contains/Equals/sort says how it compares (Ordinal for machine data).
3. Never ToUpper to compare — Equals(..., OrdinalIgnoreCase).
4. String grows in a loop → StringBuilder; joining a list → string.Join.
5. Regex that sees user input gets a timeout; JSON/HTML get real parsers.

Further reading

• Strings (C# guide)
• Best practices for comparing strings
• .NET regular expressions

The series

← Previous: 08 Modern C# 8–12 · Next: 10 Files & JSON →

Part	Topic
01	Collections
02	LINQ
03	Delegates & events
04	Async/await
05	Generics
06	Types & memory
07	Exceptions
08	Modern C# 8–12
09	Strings & text (this repo)
10	Files & JSON
11	MiniShop microservices (finale)

Author

Matej Zlatunić

License

Released under the MIT License. Feel free to use it for learning.