C++ If语句逻辑

Question

我目前正在上 C++ 类(class)，但出于某种原因，我在完成其中一项作业时遇到了一些小麻烦。

Asks a user the total amount of their purchase in a store and calculates their discount based on the following rule:

• If they spend $50, give them a 10% discount
  
• If they spend $75, the discount is 15%
  
• If they spend $100, the discount is 25%
  
• Finally, if they spend $250 or more, they get 40% off.
  
• Display the amount of their purchase, subtract the discount and display the result.

这是我到目前为止编写的代码:

#include <iostream>
using namespace std;

int main() {

    double amount,discount=0.0;
    cout<<"Enter the total amount of your purchase: $";
    cin>>amount;
    cout<<endl;

    if (amount<50)
        cout<<"You do not recieve a discount"<<endl;
    else if(amount<=50.0)
    {
        discount=0.1*amount;
        cout<<"Discount: $"<<discount<<endl;
        amount=amount*0.9;
        cout<<"Total Amount: $"<<amount<<endl;
        return 0;
    }
    else if(amount<=75.0)
    {
        discount=0.15*amount;
        cout<<"Discount: $"<<discount<<endl;
        amount=amount*0.85;
        cout<<"Total Amount: $"<<amount<<endl;
        return 0;
    }
    else if(amount<=100.0)
    {
        discount=0.25*amount;
        cout<<"Discount: $"<<discount<<endl;
        amount=amount*0.75;
        cout<<"Total Amount: $"<<amount<<endl;
        return 0;
    }
    else if(amount<=250.0)
    {
        discount=0.4*amount;
        cout<<"Discount: $"<<discount<<endl;
        amount=amount*0.6;
        cout<<"Total Amount: $"<<amount<<endl;
        return 0;
    }
    return 0;
}

我没有收到正确的数字，例如，如果我输入 74，它会给我 11.1 我觉得这是我收到错误号码的一个简单原因，但我不确定为什么

Answer 1

让我们看看您的一个问题案例:

else if(amount<=50.0)

10% 的折扣适用于花费至少 50 美元的人 - 上面使用的测试将它限制为最多花费 50 美元的人(我们暂时忽略花费少于 50 美元的人已经被过滤掉了由前面的 if).

要创建一个 if 子句来决定一个人是否应该享受 10% 的折扣，您需要对数学表达式建模:

$50.00 <= amount < $75.00

该表达式自然地转换为以下 C 代码:

else if (50.00 <= amount && amount < 75.00)

如果您愿意，可以省略该表达式的第一部分 - 它由 else 子句之前的 if 处理:

if (amount < 50.00)
    cout<<"You do not receive a discount"<<endl;
else if (amount < 75.00)
    // etc...