Question

我设法解决了大多数问题。但我仍然有这个问题。当我运行程序时，如果输出/ else。我尝试移动括号，改变if语句和所有内容。到目前为止，我们只研究了循环和if / else语句。我想做一个循环，但我想不出办法。

#include<iostream>
#include <string>

using namespace std;

int main() {
    string Cartype, rateoption;
    double total, miles, days;
    const double CdailyRate=30;
    const double PdailyRate=40;
    const double FdailyRate=50;
    const double CmileRate=0.25;
    const double PmileRate=0.35;
    const double FmileRate=0.45;

    cout<<"Thank you for choosing Car Rite Rental for your rental needs!\n"
        <<"\a Before we get started calculating your total owed please remember\n"
        <<"that here at Car Rite Rental we havea MINIMUM PAYMENT OF $30.\n\n"
        <<"Please enter the type of car you have rented: \n\n"
        <<"[please enter corresponding letter] \n"
        <<"C-Chevrolet\n"<<"P-Pontiac\n"<<"F-Ford\n";
    cin>>Cartype;
    cout<<"Please choose your payment option from the following: \n\n"
        <<"[please enter corresponding number] \n"
        <<"D-Daily Rate\n"<<"M-Mileage Rate\n";
    cin>>rateoption;

    if(rateoption=="D"||rateoption=="d") {
        cout<<"Please enter the number of days you have rented this vehicle: \n";
        cin>>days;
    } else {
        cout<<"Please enter the number of miles traveled in your rental car:\n";
        cin>>miles;
    }

    if (Cartype=="C"||Cartype=="c" && rateoption=="D"||rateoption=="d") {
        total=CdailyRate*days;
        cout<<"Your total owed today is: $"<<total<<"\nThank you again for choosing Car Rite Rental!\n";
    } else if(Cartype=="C"||Cartype=="c" && rateoption=="M"||rateoption=="m") {
        total=CmileRate*miles;
        if(total>=30)
            cout<<"Your total owed today is: $"<<total<<"\nThank you again for choosing Car Rite Rental!\n";
        else
            cout<<"Your total owed today is: $30.00\n"<<"Thank you again for choosing Car Rite Rental!\n";
    }


    if (Cartype=="P"||Cartype=="P" && rateoption=="D"||rateoption=="d") {
        total=PdailyRate*days;
        cout<<"Your total owed today is: $"<<total<<"\nThank you again for choosing Car Rite Rental!\n";
    }

    if(Cartype=="P"||Cartype=="P" && rateoption=="M"||rateoption=="m") {
        total=PmileRate*miles;
        if(total>=30)
            cout<<"Your total owed today is: $"<<total<<"\nThank you again for choosing Car Rite Rental!\n";
        else
            cout<<"Your total owed today is: $30.00\n"<<"Thank you again for choosing Car Rite Rental!\n";
    }

    return 0;
}

Answer 1

所有if语句中的条件都是错误的。在C ++表达式中，&&的优先级高于||，因此您的if语句

if (Cartype=="C"||Cartype=="c" && rateoption=="D"||rateoption=="d")

编译器可以像

那样理解

if (Cartype=="C" || (Cartype=="c" && rateoption=="D") || rateoption=="d")

但很明显，你的意思是这样理解

if ((Cartype=="C" || Cartype=="c") && (rateoption=="D" || rateoption=="d"))

因此，请修复所有这样的if语句，看看问题是否消失。

Answer 2

您需要使用括号对逻辑测试进行分组。

if (Cartype=="C"||Cartype=="c" && rateoption=="D"||rateoption=="d")

我相信你想把比较表达为：

if ((Cartype == "C" || Cartype == "c") && (rateoption == "D" || rateoption == "d"))

＆amp;＆amp;您编写的运算符不符合您的预期。

另外，请查看函数std::transform和std::tolower或std::toupper以将字符串转换为大写或小写，以便减少表达式的数量。

编辑1：嵌套if

我建议您使用嵌套 if语句：

if (Cartype=="C" || Cartype=="c")
{
    if (rateoption=="D" || rateoption=="d")
    {
        // ...
    }
    if (rateoption == "M" || rateoption=="m")
    {
        //...
    }
}
if (Cartype=="P" || Cartype=="p")
{
    if (rateoption=="D" || rateoption=="d")
    {
        // ...
    }
    if (rateoption == "M" || rateoption=="m")
    {
        //...
    }
}

为什么if语句出现在输出中。这有什么不对

2 个答案:

编辑1：嵌套if