大家好，我在下面的任务中遇到了一些麻烦。当我运行代码时，一切似乎都有效，但我在打印输出中得到的数字并不准确。不确定它是否是我的构造函数设置错误或什么。我一直在撞墙试图解决这个问题。任何帮助/建议将不胜感激！
以下是作业文字：
汽车类说明：写一个名为＆＃39; Car＆＃39;具有以下成员变量：
年。一个持有汽车模型年的int。
请。一个字符串对象，用于保存汽车的品牌。
速度。保持汽车当前速度的int对象。
此外，该类应具有以下成员函数：
构造。构造函数应该接受汽车的年份并制作成员变量。构造函数应该将这些值初始化为对象的年份并生成成员变量。构造函数应该将速度成员变量初始化为0.
存取器。应创建适当的访问器函数，以允许从对象的年份，制造和加速成员变量中检索值。
加速。加速函数应在每次调用时向速度成员变量添加5。
刹车。每次调用时，制动功能应从速度成员变量中减去5。在创建Car对象的程序中演示类，然后调用加速函数五次。每次调用加速功能后，获取当前车速并显示。然后，调用制动功能5次。每次调用制动功能后，获取当前车速并显示它。
#include <iostream>
#include <string>
using namespace std;
class Car
{
private:
int year;
string make;
int speed;
public:
Car(int, string, int);
int getSpeed();
int getModel();
void accelerate();
void brake();
};
int Car::getSpeed()
{
return speed;
}
Car::Car(int year, string make, int speed = 0 )
{
}
void Car::accelerate()
{
speed +=5;
}
void Car::brake()
{
if( speed > 5 )
speed -=5;
else speed = 0 ;
}
int main ()
{
int year;
string make;
cout << "Please enter the model year of the car.\n";
cin >> year ;
cout << "Please enter the make of the car.\n";
cin >> make ;
Car myCar(year,make);
int i = 0;
for (; i<5; ++i)
{
myCar.accelerate();
cout << "Accelerating.\n" << "The current speed of the car is: " << myCar.getSpeed()<<endl;
}
{
int j = 0;
for (; j<5; ++j)
{
myCar.brake();
cout << "Decelerating.\n" << "The current speed of the car is: " << myCar.getSpeed()<<endl;
}
return (0);
}
}
答案 0 :(得分：1)
此构造函数
Car::Car(int year, string make, int speed = 0 )
{
}
没有初始化。它有一个空体，没有初始化成员列表。此外，根据赋值，构造函数必须有两个参数。
它可以看作以下方式
在课程定义中
inline Car( int year, std::string & make );
以及构造函数本身的定义
Car::Car( int year, const std::string make ) : year( year ), make( make ), speed( 0 )
{
}
可以将访问器声明为
int getYear() const;
int getSpeed() const;
const std::string & getModel() const;
^^^^^^^^^^^^^^^^^^^
答案 1 :(得分：1)
构造函数
Car::Car(int year, string make, int speed = 0 )
{
}
没有做你所描述的。这三个参数（year，make和speed）与Car成员的名称相同，但它们是单独的变量。
结果是Car成员是默认构造的，main()传递的值实际上被忽略了。
为了使事情更清楚，请为参数指定不同的名称，并在初始化列表中初始化成员。
Car::Car(int y, string m, int s) : year(y), make(m), speed(s)
{
}
允许参数与类成员具有相同的名称，但这往往更难以阅读，即更容易误解代码正在做什么。在您的情况下，您认为给出与类成员同名的参数用于初始化类成员，这是完全错误的。无论哪种方式，构造函数都需要使用参数显式初始化成员，否则类成员会接收默认值（而不是传递的值）。
此外，如果您希望参数具有默认值，请在类的定义中指定它，而不是在构造函数的定义中指定。例如;
class Car
{
public:
Car(int, std::string, int = 0);
};
Car::Car(int y, string m, int s) : year(y), make(m), speed(s)
{
}
这使事情变得更容易，特别是如果类定义在头文件中。
答案 2 :(得分：0)
#include "stdafx.h"
#include <iomanip>
#include <iostream>
#include<stdio.h>
#include <cstdlib>
#include <string>
#include <iomanip>
double getaccelarate(double &, double &);
double getbrake(double &, double &);
double getcruise(double &, double &);
void outputStatusHeader();
void demo();
double updateDistanceTraveled(double &, double &);
int delta = 5;
//double brakee = 0;
double previousSpeed = 0;
double currentSpeed = 0;
using namespace std;
int main()
{
char command;
//The amount of elapsed time for each calculation interval
(fixed at 1 second)
const int timeInterval = 1;
//double currentSpeed=0;
//convert into the distance travelled by feet
int totalFeetTraveled = 0;
//the average speed travel
int averageSpeed = 0;
//double previousSpeed =0;
int averageSpeed_FeetPerSecond = 0;
int intervalFeetTraveled = 0;
int speed = 0;
//the amount of time that the time will increase by
//const int delta= 5;
while (true)
{
cout << "Command:";
cin >> command;
switch (command)
{
case 'a':
//double accelarate;
double speed;
speed = getaccelarate(currentSpeed, previousSpeed);
//cout << getaccelarate;
cout << "Accelerate"<<setw(20)<<"Accelerating"<<setw(5);
cout << speed;
double conve;
conve = updateDistanceTraveled(previousSpeed,
currentSpeed);
cout <<setw(10)<<setprecision(3)<<conve<<endl;
//updateDistanceTraveled(previousSpeed,currentSpeed);
break;
case 'b':
double brake;
brake = getbrake(previousSpeed, currentSpeed);
cout << "Brake" <<setw(20)<<"Braking"<<setw(5);
cout << brake;
//double brake1 = 0;
//brake1 = updateDistanceTraveled(previousSpeed,
currentSpeed);
cout << setw(10) << setprecision(3) << conve << endl;
break;
case 'c':
double cruise;
cruise = getcruise(previousSpeed, currentSpeed);
cout << "Cruise" << setw(20) << "Cruising" << setw(5);
cout << cruise;
cout << setw(10) << setprecision(3) << conve << endl;
break;
case 'h':
outputStatusHeader();
break;
case 'd':
demo();
break;
case 'q':
cout << " Exit program";
exit(1);
break;
default:
cout << "Invalid command" << endl;
break;
}
}
system("pause");
return 0;
}
//converting mph to feet perhours
double updateDistanceTraveled(double &previousSpeed,double ¤tSpeed)
{
//getaccelarate(previousSpeed, currentSpeed);
double averageSpeed = 0;
double averageSpeed_FeetPerSecond = 0;
double intervalFeetTraveled=0;
//double totalFeetTraveled=0;
const int timeInterval = 1;
averageSpeed = (previousSpeed + currentSpeed) / 2;
averageSpeed_FeetPerSecond = averageSpeed * 5280.0 / 3600.0;
intervalFeetTraveled = averageSpeed_FeetPerSecond * timeInterval;
return intervalFeetTraveled;
/*totalFeetTraveled = totalFeetTraveled + intervalFeetTraveled;
return totalFeetTraveled;*/
}
//to decrease speed
double getbrake(double &previousSpeed, double ¤tSpeed)
{
previousSpeed = currentSpeed;
currentSpeed -= delta;
return currentSpeed;
}
//to increase speed
double getaccelarate(double &previousSpeed, double ¤tSpeed)
{
previousSpeed = currentSpeed;
currentSpeed = currentSpeed + delta;
return currentSpeed;
}
// to stay in current speed
double getcruise(double &previousSpeed, double ¤tSpeed)
{
previousSpeed = currentSpeed;
return previousSpeed;
}
//unfinished demo
void demo()
{
cout << "Function Current State Current Speed Interval Distance
Total Feet (and miles) traveled" << endl;
cout << "-----------------------------------------------------------------------------------" << endl;
for (int x = 1; x < 4; x++)
{
double speed;
speed = getaccelarate(currentSpeed, previousSpeed);
//cout << getaccelarate;
cout << "Accelerate" << setw(20) << "Accelerating" << setw(5);
cout << speed;
double conve;
conve = updateDistanceTraveled(previousSpeed, currentSpeed);
cout << setw(10) << setprecision(3) << conve << endl;
}
}
//for supported commands
void outputStatusHeader()
{
cout << " supported commands\n"
<< " a accelerate\n"
<< " b brake\n"
<< " c cruise\n"
<< " d demo\n"
<< " h print this help text\n"
<< " q quit(end the program)"
<< endl;
}
{
cout << " supported commands\n"
<< " a accelerate\n"
<< " b brake\n"
<< " c cruise\n"
<< " d demo\n"
<< " h print this help text\n"
<< " q quit(end the program)"
<< endl;
}