如何返回多个矢量对象的平均值?C++

嗨，我对 c++ 很陌生，我有一个项目，但要做，但项目中的一个问题需要我添加一个函数 getAverageCostPerDay((，它采用 Reservations 对象的向量并返回汽车预订的平均成本。我该怎么做？谢谢

预订。

#pragma once
#include <string>
class Reservation
{
private:
int id;
std::string name;
int stDate;
int stMonth;
int stYear;
int duration;
float cost;
std::string licensePlate;
static int reservationCount;
public:
//Constructor
Reservation();
Reservation(int id, std::string name, int stDate, int stMonth, int
stYear, int duration, float cost, std::string licensePlate);
//Destructor
~Reservation();
//Getters
int getId();
std::string getName();
int getStDate();
int getStMonth();
int getStYear();
int getDuration();
float getCost();
std::string getLicensePlate();
//Setters
void setId(int id);
void setName(std::string name);
void setStDate(int stDate);
void setStMonth(int stMonth);
void setStYear(int stYear);
void setDuration(int duration);
void setCost(float cost);
void setLicensePlate(std::string licensePlate);
static int getReservationCount()
{
return reservationCount;
}
};

预订.cpp

#include "pch.h"
#include "Reservation.h"
int Reservation::reservationCount = 0;
//Constructor
Reservation::Reservation()
{
this->id = 0;
this->name = "";
this->stDate = 0;
this->stMonth = 0;
this->stYear = 0;
this->duration = 0;
this->cost = 0;
this->licensePlate = "";
reservationCount++;
}
Reservation::Reservation(int id, std::string name, int stDate, int stMonth, 
int stYear, int duration, float cost, std::string licensePlate)
{
this->id = id;
this->name = name;
this->stDate = stDate;
this->stMonth = stMonth;
this->stYear = stYear;
this->duration = duration;
this->cost = cost;
this->licensePlate = licensePlate;
reservationCount++;
}
//Destructor
Reservation::~Reservation()
{
reservationCount--;
std::cout << "Destroying (" << this->name << ")" << std::endl;
}
//Getters
int Reservation::getId()
{
return this->id;
}
std::string Reservation::getName()
{
return this->name;
}
int Reservation::getStDate()
{
return this->stDate;
}
int Reservation::getStMonth()
{
return this->stMonth;
} 
int Reservation::getStYear()
{
return this->stYear;
}
int Reservation::getDuration()
{
return this->duration;
}
float Reservation::getCost()
{
return this->cost;
}
std::string Reservation::getLicensePlate()
{
return this->licensePlate;
}
//Setters
void Reservation::setId(int id)
{
this->id = id;
}
void Reservation::setName(std::string name)
{
this->name = name;
}
void Reservation::setStDate(int stDate)
{
this->stDate = stDate;
}
void Reservation::setStMonth(int stMonth)
{
this->stMonth = stMonth;
}
void Reservation::setStYear(int stYear)
{
this->stYear = stYear;
}
void Reservation::setDuration(int duration)
{
this->duration = duration;
}
void Reservation::setCost(float cost)
{
this->cost = cost;
}
void Reservation::setLicensePlate(std::string licensePlate)
{
this->licensePlate = licensePlate;
}

主.cpp

#include "pch.h"
#include "Reservation.h"
//Regular Expressions
std::string idRegexStr = "[0-9]{3,4}";
std::string nameRegexStr = "[A-Za-z]{1}[a-z]{1,30} [A-Za-z]{1}[a-z]{1,30}";
std::string stDateRegexStr = "[0-3]{1}[0-9]{1}";
std::string stMonthRegexStr = "[0-1]{1}[0-9]{1}";
std::string stYearRegexStr = "[1-2]{1}[0-9]{1}[0-9]{1}[0-9]{1}";
std::string durationRegexStr = "[1-9]{1}[0-9]{1}";
std::string costRegexStr = "[0-9]{2}.[0-9]{2}";
std::string licencePlateRegexStr = "[0-9]{2,3}\s*[A-Z]{2,3}\s*[0-9]+";
//Validates data against a user-defined string
bool validate(std::string regexStr, std::string data)
{
return std::regex_match(data, std::regex(regexStr));
}
std::vector<Reservation>populateVector(Reservation defaultVector, int size)
{
std::vector<Reservation> outVector;
for (int i = 0; i < size; i++)
{
outVector.push_back(defaultVector);
}
return outVector;
}
double getAverageCostPerDay(const std::vector<Reservation> outVector)
{
double average = 0;
for (std::size_t i = 0; i < outVector.size(); i++)
{
average = std::vector<Reservation>outVector.at(float cost);
}
return true;
}
int main()
{
/*
//these were example values to see if regex works
bool idIsValid = validate(idRegexStr, "101");
bool nameIsValid = validate(nameRegexStr, "John Smith");
bool stDateIsValid = validate(stDateRegexStr, "24");
bool stMonthIsValid = validate(stMonthRegexStr, "10");
bool stYearIsValid = validate(stYearRegexStr, "2018");
bool durationIsValid = validate(durationRegexStr, "10");
bool costIsValid = validate(costRegexStr, "22.50");
bool licenseIsValid = validate(licencePlateRegexStr, "181 LH 555");
std::cout << "Invalid = 0 / Valid = 1n";
std::cout << "n";
std::cout << "Valid ID: " << idIsValid << std::endl;
std::cout << "Valid Name: " << nameIsValid << std::endl;
std::cout << "Valid Start Date: " << stDateIsValid << std::endl;
std::cout << "Valid Start Month: " << stMonthIsValid << std::endl;
std::cout << "Valid Start Year: " << stYearIsValid << std::endl;
std::cout << "Valid Duration: " << durationIsValid << std::endl;
std::cout << "Valid Cost: " << costIsValid << std::endl;
std::cout << "Valid License: " << licenseIsValid << std::endl;
*/
Reservation r1(101, "John Smith", 24, 10, 2018, 4, 22.50, "181 LH 
5555");
Reservation r2(102, "Jane Caroll", 31, 01, 2017, 6, 34.25, "161 DUB 
55454");
Reservation r3(103, "Sean Morrissey", 16, 06, 2014, 2, 67.50, "162 WEX 
83675");
Reservation r4(104, "Billy Joe", 04, 03, 2016, 8, 51.20, "152 DUB 
10347");
std::cout << "Reservation Count: " << Reservation::getReservationCount() 
<< 
std::endl;
}