Given the expression: 

n = 10

that has both rvalue and lvalue expressions, a useful heuristic to determine whether an expression is lvalue is to ask if you can take its address. If you can, it typically is a lvalue expression. If you can't, it's usually a rvalue expression. So, in the expression n = 10, we have one lvalue expression n and two rvalue expressions: 10 and n=10.

Just remember that in C, built-in pre-increment/decrement operators, comma operator, ternary or conditional ?: operator evaluate to an rvalue. In C++ these operators evaluate to an lvalue.

When the expression is a function call or a call to an overloaded operator, the answer to the question what kind of value? is not so obvious. If the definition or declaration is available, it's possible to answer the question. For other expressions such as ++i involving the built-in pre-increment operator, you now know that the operator requires an lvalue operand and evaluates to an lvalue expression.

Consider the following C++ code. Write if the code doesn't compile. Write if the code causes undefined behavior at run time. Write if an unspecified value is written to standard output. Otherwise, write the exact text written to the standard output stream.

int main() {
  int i{};
  ++i = 5;
  std::cout << i;
}