All 16 Fundamentals questions
More in Fundamentals
What are auto-implemented properties, and what does the compiler generate behind the scenes for one? What is the difference between checked and unchecked arithmetic? What is the difference between out, ref and in parameters? How do 'ref', 'out', and 'in' parameter modifiers differ in how they pass arguments to a method? How do expression-bodied members simplify simple method, property, and constructor definitions? How does string interpolation compile, and when should you avoid it? How does pattern matching in an 'is' expression differ from a traditional type check with 'as' and a null check, and what does it enable? How does the C# compiler enforce 'definite assignment' analysis, and what compile error results from violating it? How do C# 12's primary constructors on regular classes (not just records) change how you write simple constructor-and-field boilerplate? How does the C# 'nameof' operator work, and why is it preferred over hardcoding a string literal for things like argument names in exceptions?
Advertisement
C# › Fundamentals

How does string interpolation work, and how does it compare to string.Format() and simple concatenation?

Intermediate

Answer

String interpolation (`$"..."`) embeds expressions directly inside `{}` within a string literal, compiled internally into either a string.Format() call or (in modern .NET) a more efficient interpolated string handler — it's generally more readable than string.Format()'s positional placeholders and avoids the performance pitfalls of repeated '+' concatenation in a loop.
string name = "Sam";
int age = 30;
string message = $"{name} is {age} years old."; // readable, compiler-optimized

// Equivalent, more verbose alternatives:
string message2 = string.Format("{0} is {1} years old.", name, age);
string message3 = name + " is " + age + " years old.";
Real-world example Building a readable, formatted log message or user-facing display string combining multiple variable values.

Common follow-ups: Why is repeated string concatenation with '+' inside a LOOP specifically discouraged, in favor of StringBuilder?

String Handling & StringBuilder
All 16 Fundamentals questions