Explaining the difference between a statement and an expression in c++

Question

I am trying to understand thoroughly the difference between a statement and an expression
But i am finding it confusing even after reading this answer Expression Versus Statement
look at the following:

std::cout << "Hello there? " ;  

I could say that it is a statement as it is ending with a semi- colon BUT i could also say
It is an expression since i have an ostream , an output operator and a string literal
and this expression yields a value which is the left hand operand.
Which one is correct?

Answer 1

Let's see what the C++ grammar can tell us:

statement:
  labeled-statement
  attribute-specifier-seq_opt expression-statement
  attribute-specifier-seq_opt compount-statement
  attribute-specifier-seq_opt selection-statement
  attribute-specifier-seq_opt iteration-statement
  attribute-specifier-seq_opt jump-statement
  declaration-statement
  attribute-specifier-seq_opt try-block

expression-statement:
  expression_opt ';'

So it is a statement; in particular, an "expression statement", which consists of a (potentially empty) expression followed by a semi-colon. In other words,

std::cout << "Hello there? "

is an expression, while

std::cout << "Hello there? " ;

is a statement.