C++ Please

Write a function named mean that accepts as a parameter a reference to a vector of real numbers, and returns the arithmetic mean (average) of the integers in the vector as a real number. For example, if the vector passed contains {2.0, 4.5, 6.5, 1.0}, your function should return 3.5. If the vector is empty, return 0.0. Do not modify the vector that is passed in.