Summary

Conclusions

Every value in C# has a type known at compile time. Value types (numbers, bool, char, structures) store values directly, while reference types (string, object, arrays, classes) store references to objects on the managed heap. The main integer type is int, or long for large values; use double for fractional calculations and decimal for money, as it avoids decimal fraction representation errors. Safe type conversions happen implicitly, while conversions that may lose data require an explicit cast or the Convert, Parse, or TryParse methods. When evaluating expressions, account for integer division, overflow, operator precedence, and the rounding mode; represent potentially absent values using types with ? and handle them with ?? and ??=.

Self-check questions

1. How do value types differ from reference types? Give examples.
2. What happens when assigning value-type and reference-type variables?
3. What are boxing and unboxing? When does InvalidCastException occur?
4. Which integer types does C# provide? How can you find a type's range?
5. How do you write hexadecimal and binary literals? What are the L, U, f, and m suffixes for?
6. How do float, double, and decimal differ? Which type should you choose for money?
7. Why does 0.1 + 0.2 == 0.3 produce False? How should you compare floating-point numbers?
8. What are NaN and infinity? How can you check whether a value is NaN?
9. How does implicit typing with var work? When should you use it?
10. How does a const constant differ from a variable?
11. What do int? and string? mean? How do ?? and ??= work?
12. Which type conversions happen implicitly? When is an explicit cast needed?
13. How do (int)3.5, Convert.ToInt32(3.5), and Math.Round(3.5) differ?
14. How do integer division and % work?
15. What is the difference between prefix and postfix increment?
16. What is overflow? How can you detect it with checked?
17. What is short-circuit evaluation of && and ||?
18. How do you test, set, and clear a bit using bitwise operators?

Useful links

• C# built-in types: https://learn.microsoft.com/dotnet/csharp/language-reference/builtin-types/built-in-types
• Integer types: https://learn.microsoft.com/dotnet/csharp/language-reference/builtin-types/integral-numeric-types
• Floating-point types: https://learn.microsoft.com/dotnet/csharp/language-reference/builtin-types/floating-point-numeric-types
• Numeric conversions: https://learn.microsoft.com/dotnet/csharp/language-reference/builtin-types/numeric-conversions
• Operators and expressions: https://learn.microsoft.com/dotnet/csharp/language-reference/operators/
• checked and unchecked statements: https://learn.microsoft.com/dotnet/csharp/language-reference/statements/checked-and-unchecked
• Nullable types: https://learn.microsoft.com/dotnet/csharp/nullable-references
• Standard numeric formats: https://learn.microsoft.com/dotnet/standard/base-types/standard-numeric-format-strings