Although Rust doesn't have either ++ increment operator, it does have both the assignment = and the add-assign += and they're both expressions because almost everything in Rust is an expression.

Crucially however these expressions have the unit type () aka the empty tuple as their result, ruling out hard to follow C like int a = 1 + (b = 2 + (c = d * 3));

Similarly the "Oops I wrote = instead of ==" gets so rare as to be negligible when you stop coercing everything to a boolean. In Rust only true is true and only false is false. So when you write if k = 5 rather than checking if k == 5 that's a type error. The expression k == 5 is a boolean, that would be fine, but the expression k = 5 is just () and that's neither true nor false it's just the wrong type.