c ++：if语句无法正常运行并继续进行无效输出

Question

刚开始学习 C++ 并尝试制作一个自动订购系统，但是在尝试运行继续使用它之前我遇到了这个问题：

#include <iostream>
using namespace std;

char acoustic, fender, hartwood, electric, gibson, ibanez, drums, pearl, 
roland, piano, casio;
char rolandpi, equip, string, headphone, amp, mixer, micro, tuner, pick, 
music, Yes, No;

int pay1 = 0, pay2 = 0;

int main()
{
    cout << "Welcome to the Music Shop" << endl <<endl;

    cout << "a. Acoustic Guitar" << endl;
    cout << "a.1 Fender Acoustic Guitar   - P6,900.00" << endl;
    cout << "a.2 Hartwood Acoustic Guitar - P6,300.00" << endl <<endl;

    cout << "b. Electric Guitar" << endl;
    cout << "b.1 Gibson Electric Guitar   -P8,500.00" << endl;
    cout << "b.2 Ibanez Electric Guitar   -P25,000.00" << endl <<endl;

    cout << "c. Drums" << endl;
    cout << "c.1 Pearl Drum Kits          -P27,000.00" << endl;
    cout << "c.2 Roland Electronic Drums  -P24,000.00" << endl <<endl;

    cout << "d. Piano" << endl;
    cout << "d.1 Casio Digital Piano      -P19,000.00" << endl;
    cout << "d.2 Roland Piano             -P120,000.00" << endl <<endl;

    cout << "e. Music Equipments" << endl;
    cout << "e.1 Guitar String            -P113.00" << endl;
    cout << "e.2 Headphones               -P1,600.00" << endl;
    cout << "e.3 Amplifier                -P2,800.00" << endl;
    cout << "e.4 Digital Mixer            -P4,750.00" << endl;
    cout << "e.4 Vocal Microphone         -P860.00" << endl;
    cout << "e.5 Guitar Tuner             -P537.00" << endl;
    cout << "e.6 Guitar Pick              -P360.00" << endl <<endl;

    cout << "Choose the music instrument or equipment you want to buy: ";
    cin >> music;

    switch (music)
    {
        case 'a':

        cout<< "Acoustic Guitar" << endl;
        cout<< "1. Fender Acoustic Guitar   - P6,900.00" << endl;
        cout<< "2. Hartwood Acoustic Guitar - P6,300.00" << endl <<endl;
        cout<<"Choose from the available Acoustic Guitars:";
        cin>>acoustic;

        if (acoustic == 1){
            cout<<"Enter your payment:";
            cin>>pay1;
            if (pay1=6900){
                cout<<"You have succesfully purchased Fender Acoustic Guitar"<<endl;
            }
                else if (pay1>6900){
                    pay1 -= 6900;
                    cout<<"Your change is:"<<pay1<<endl;
                }
                    else (pay1<6900);
                    {
                        cout<<"You do not have enough money"<<endl;
                    }
        }
        else if (acoustic == 2){
            cout<<"Enter your payment:";
            cin>>pay1;
            if (pay1=6300){
                cout<<"You have succesfully purchased Fender Acoustic Guitar"<<endl;
            }
                else if (pay1>6300){
                    pay1 -= 6300;
                    cout<<"Your change is:"<<pay1<<endl;
                }
                    else (pay1<6300);
                    {
                        cout<<"You do not have enough money"<<endl;
                    }
        }
        else {
            cout<<"Invalid"<<endl;
        }
    }
}

我已经检查了我的 if else 语句，但找不到问题所在。

从 "Choose from the available Acoustic Guitars" 输入 1 或 2 后，它继续进行到 "invalid"。

Answer 1

您在此处阅读 char：

cout << "Choose from the available Acoustic Guitars:";
cin >> acoustic;

但随后你将它与一行后的 int 进行比较：

if (acoustic == 1) {

这应该是：

if (acoustic == '1') {

还有这个：

if (pay1 = 6900) {

应该是：

if (pay1 == 6900) {

否则无论输入什么你都会得到不正确的输出，因为pay1 = 6900将pay1设置为6900和returns6900，这是隐式转换为 true.

还有这一行：

else (pay1 < 6900);

需要改为

else if (pay1 < 6900)

因为否则 (pay1 < 6900) 不是 if 语句的条件，而是 (pay1 < 6900); 是 else 情况下发生的情况（它只是计算一个布尔值和丢弃它），导致始终打印以下 "You do not have enough money" 消息。

Answer 2

@Blaze 非常感谢你，现在我快完成了，现在我在输入 Yes 后遇到 Yes 或 No 的问题，程序刚刚结束，我不知道它有什么问题 >.<

cout<<"\nWould you like to buy an Electric Guitar?"<<endl;
    cout<<"Yes or No?"<<endl;
    cin>>answer;

    if (answer == Yes){
    cout<< "Electric Guitar" << endl;
    cout<< "1. Gibson Electric Guitar   -P8,500.00" << endl;
    cout<< "2. Ibanez Electric Guitar   -P25,000.00" << endl <<endl;
    cout<<"Choose from the available Electric Guitars:";
    cin>>electric;

        if (electric=='1'){
        cout<<"Enter your payment:";
        cin>>pay2;
        if (pay2==8500){
            cout<<"You have succesfully purchased Fender Acoustic Guitar"<<endl;
        }
            else if (pay2>8500){
                pay2 -= 8500;
                cout<<"Your change is:"<<pay2<<endl;
            }
                else if(pay2<8500)
                {
                    cout<<"You do not have enough money"<<endl;
                }   
    }
    else if (electric=='2'){
        cout<<"Enter your payment:";
        cin>>pay2;
        if (pay2==25000)
        {
            cout<<"You have succesfully purchased Fender Acoustic Guitar"<<endl;
        }
            else if (pay2>25000){
                pay2 -= 25000;
                cout<<"Your change is:"<<pay2<<endl;
            }
                else if (pay2<25000)
                {
                    cout<<"Invalid"<<endl;
                }   
    }
    else {
        cout<<"Invalid";
    }
} 
    else if (No){
        cout<<"Thank you for checking our other products";
}
}
}

c ++：if语句无法正常运行并继续进行无效输出

c++ : The if statement not functioning correctly and proceeds to Invalid output

c++

if-statement

char

comparison-operators