C++ 如何在if语句中使用特定的Void函数 #包括 使用名称空间std； 等级车辆 { 公众： 空心车轮（）{ cout>wh； 如果（wh==2）{ cout

在不同的类和不同的函数之间有很多方法与变量交互。正如@TheUndeadFish所提到的，返回值是一个很好的起点。如果你一心想使用空函数，一个选择就是在你的Vehicles类中使用一个公共变量，你在wheels函数中设置了该变量

因此，您的车辆等级将变为：

#include <iostream>
using namespace std;

class Vehicles
{

public:

void wheels () {
cout << "Enter number of wheels: ";
int wh;
cin >> wh;

if (wh == 2) {
    cout << "You chose a Motorcycle!\n";
} else if (wh == 3) {
    cout << "You chose a Tricycle!\n";
} else if (wh == 4) {
    cout << "You chose a Car!\n";
}
}
} ; //number of wheels chosen

class brandMotorcycle : public Vehicles
{
public:

void brandM () {
cout << "Enter brand: \n 1: Yamaha \n 2: Ducati \n 3: Honda \n 4: Kawasaki \n 5: Suzuki \n";
int br;
cin >> br;

if ( br == 1) {
    cout << "You chose Yamaha! \n";
} else if (br == 2) {
    cout << "You chose Ducati! \n";
} else if (br == 3) {
    cout << "You chose Honda! \n";
} else if (br == 4) {
    cout << "You chose Kawasaki! \n";
} else if (br == 5) {
    cout << "You chose Suzuki! \n";
}
}
} ; //brand of motorcycle in case the user will chose 2 wheels

class brandTricycle : public Vehicles
{
public:

void brandT () {
cout << "Enter brand: \n 1: Classic \n 2: CATs \n 3: KYTO \n 4: Prime Green \n 5: Sun Etrike \n";
int br;
cin >> br;

if ( br == 1) {
    cout << "You chose Classic! \n";
} else if (br == 2) {
    cout << "You chose CATs! \n";
} else if (br == 3) {
    cout << "You chose KYTO! \n";
} else if (br == 4) {
    cout << "You chose Prime Green! \n";
} else if (br == 5) {
    cout << "You chose Sun Etrike! \n";
}
}
} ; //brand of tricycle in case the user chose 3 wheels

class brandCar : public Vehicles
{
public:

void brandC () {
cout << "Enter brand: \n 1: Mazda \n 2: Honda \n 3: Toyota \n 4: Kia \n 5: Volkswagen \n";
int br;
cin >> br;

if ( br == 1) {
    cout << "You chose Mazda! \n";
} else if (br == 2) {
    cout << "You chose Honda! \n";
} else if (br == 3) {
    cout << "You chose Toyota! \n";
} else if (br == 4) {
    cout << "You chose Kia! \n";
} else if (br == 5) {
    cout << "You chose Volkswagen! \n";
}
}
} ; //brand of cars in case the user chose 4 wheels

int main () {

Vehicles number;
brandMotorcycle brandM;
brandTricycle brandT;
brandCar brandC;
number.wheels();

    if (wheels == 2) {
brandM.brandM();
} else if (wheels == 3) {
brandT.brandT();
}  else if (wheels == 4) {
brandC.brandC();
} // this part is my problem

return 0;
}

---

编辑：请注意，如果注释掉对number.wheels（）的调用，您将得到一个未初始化的变量错误。实际上，您希望它初始化（可能是-1）在Vehicles类构造函数中，以避免出现此错误。

您正在

wheels

中收集数据，以便在返回时使用这些数据。因此，是时候阅读函数的返回值了。非常感谢，联机类非常困难。

class Vehicles
{

public:
    int wh;

    void wheels() {
        cout << "Enter number of wheels: ";
        cin >> wh;

        if (wh == 2) {
            cout << "You chose a Motorcycle!\n";
        }
        else if (wh == 3) {
            cout << "You chose a Tricycle!\n";
        }
        else if (wh == 4) {
            cout << "You chose a Car!\n";
        }
    }
}; //number of wheels chosen

int main() {

    Vehicles number;
    brandMotorcycle brandM;
    brandTricycle brandT;
    brandCar brandC;
    number.wheels();

    int wheels = number.wh;
    if (wheels == 2) {
        brandM.brandM();
    }
    else if (wheels == 3) {
        brandT.brandT();
    }
    else if (wheels == 4) {
        brandC.brandC();
    } // this part is my problem

    return 0;
}