Expression Versus Statement

Question

I\'m asking with regards to c#, but I assume its the same in most other languages.

Does anyone have a good definition of expressions and statements

Answer 1

Most precisely, a statement must have a "side-effect" (i.e. be imperative) and an expression must have a value type (i.e. not the bottom type).

The type of a statement is the unit type, but due to Halting theorem unit is fiction so lets say the bottom type.

---

Void is not precisely the bottom type (it isn't the subtype of all possible types). It exists in languages that don't have a completely sound type system. That may sound like a snobbish statement, but completeness such as variance annotations are critical to writing extensible software.

Let's see what Wikipedia has to say on this matter.

https://en.wikipedia.org/wiki/Statement_(computer_science)

In computer programming a statement is the smallest standalone element of an imperative programming language that expresses some action to be carried out.

Many languages (e.g. C) make a distinction between statements and definitions, with a statement only containing executable code and a definition declaring an identifier, while an expression evaluates to a value only.