C# Null and Nullable Values

A survey score of 0 may mean the respondent chose the lowest score. If the respondent has not answered, storing 0 destroys that distinction. null represents the absence of a value, allowing the program to handle ‘not supplied’ separately from valid domain values.

The same distinction appears in text: an empty string means a string exists with no characters, whitespace contains characters that may display blank, and null means no string reference. Which states are valid depends on the domain rather than the type alone.

Value types such as int and DateTime normally always contain a value. Adding ? creates a nullable value type: int? can hold an integer or null. HasValue checks presence, Value retrieves the value but throws when absent, and GetValueOrDefault returns a fallback.

The ?? operator chooses a fallback only when the left side is null. A default is appropriate when the domain defines one. Using 0 for every missing number can quietly turn unknown data into a real measurement, so name or explain the policy.

decimal? discount = null;
decimal appliedDiscount = discount ?? 0m;

Console.WriteLine(appliedDiscount);

0

In modern .NET projects with nullable reference types enabled, string means the code intends a non-null reference and string? means null is expected. The compiler tracks assignments and warns when a possible null is dereferenced. This feature improves design feedback; it does not make the runtime incapable of producing null.

The null-conditional operator ?. accesses a member only when the receiver is non-null and otherwise produces null. The null-forgiving operator ! silences a warning without adding a runtime check. Use ! only when you have evidence the compiler cannot see, not as a shortcut around unclear state.

string? nickname = FindNickname();
int length = nickname?.Length ?? 0;

// FindNickname would be another method that may return null.

If a customer must have a name, validate the input before creating the customer and store a non-null string afterward. Carrying string? through every later method forces the entire program to account for a state the domain says should not exist.

When absence is meaningful, keep it visible in the type and handle it close to the decision that understands what it means. A user interface may display Not provided; a calculation may skip the record; a required export may reject it. There is no universal fallback.