Return void type in C and C++

C11, 6.8.6.4 “The return statement”:

A return statement with an expression shall not appear in a function whose return type is void.

No, you may not use an expression, even if it is of void type.

From the foreword of the same document:

Major changes in the second edition included:

[…]

• return without expression not permitted in function that returns a value (and vice versa)

So this was a change from C89 -> C99 (the second edition of the language standard), and has been that way ever since.

C++14, 6.6.3 “The return statement”:

A return statement with an expression of non-void type can be used only in functions returning a value […]
A return statement with an expression of type void can be used only in functions with a return type of cv
void; the expression is evaluated just before the function returns to its caller.

Yes, you may use an expression if it is of void type (that’s been valid since C++98).