Question

#include <iostream>
#include <string>

using namespace std;


int main ()
{
//Get Seed Color
string seedColor = "";
cout << "Enter Your Seed's Color: \n";
cin >> seedColor;
// Get Temp

if(seedColor != "red" || seedColor != "Red" && seedColor != "blue" || seedColor != "Blue")
    {
    cout << "Invalid Response. Please enter Red or Blue for the Color.\n";
    return 0;
    }

int temp = 0;
cout << "Enter Your Seed's Temperature: ";
cin >> temp;

 // if Red Seed
if(seedColor == "Red"|| seedColor == "red")
{


    //if temp >= 75
    if (temp >= 75)
    {

         // Get Soil Moisutre
        string soilMoisture = "";
        cout << "Enter Your Soil's Moisture (Wet or Dry): ";
        cin >> soilMoisture;

        // Soil Dry Output Dandelion
        if (soilMoisture == "Wet" || soilMoisture == "wet" )
        {
            cout << "A Sunflower will grow!\n";
        }

        if (soilMoisture == "Dry" || soilMoisture == "dry")
        {
            cout << "A Dandelion will grow!\n";
        }
    }


    else
    {
       // Otherwise Mushroom
       cout << "You will have a Mushroom!";
    }



}
// if Blue seed
if (seedColor == "Blue" || seedColor == "blue")
{


    //if temp b/t 60 && 70
    if (temp >= 60 && temp <= 70)
    {
        // Get Soil Moisutre
        string soilMoisture = "";
        cout << "Enter Your Soil's Moisture (Wet or Dry): ";
        cin >> soilMoisture;

        // Soil Dry Output Sunflower
        if (soilMoisture == "Dry" || soilMoisture == "dry")
        {
            cout << "A Sunflower will grow!";
        }
        // Soil Wet Output Dandelion
        if (soilMoisture == "Wet" || soilMoisture == "wet")
        {
            cout << "A Dandelion will grow! \n";
        }

    }
    else
    {
        // Otherwise Mushroom
        cout << "You will have a Mushroom! \n";
    }


}
    return 0;
}

嘿伙计们，所以我在尝试解决这个问题时遇到了一些麻烦。每当我运行此代码时，无论我是否放置＆＃34; Red＆＃34; ＆＃34;蓝色＆＃34;甚至像香蕉＆＃34;香蕉＆＃34;它给了我＆＃34;无效的响应＆＃34;提示。任何想法如何解决这个问题？

Answer 1

if(seedColor != "red" || seedColor != "Red" && seedColor != "blue" || seedColor != "Blue")

首先可能更容易为可接受的种子颜色重写if。我们知道什么是好的，对于许多程序员来说，＆＃34; good＆＃34;条件是最容易设想的：

if( seedColor == "red" || seedColor == "Red" || 
    seedColor == "blue" || seedColor == "Blue")
{
   // this is a good seed color
}
else
{
   // this is a bad seed color
}

现在，如果你真的想测试糟糕的种子颜色，那么只需要在整个条件下放置一个!就可以了：

if(!(seedColor == "red" || seedColor == "Red" || 
    seedColor == "blue" || seedColor == "Blue") )
{
   // this is a bad seed color
}
else
{
   // this is a good seed color
}

有一个名为Demorgan's Law的定理：http://en.wikipedia.org/wiki/De_Morgan%27s_laws

在此处应用它将产生以下结果：

if (seedColor != "red" && seedColor != "Red" && 
    seedColor != "blue" && seedColor != "Blue")
{
   // this is a bad seed color
}
else
{
   // this is a good seed color
}

换句话说，==转为!=，||转为&&。基本上，根据您关于!=的问题，我们使用了3个步骤来提出所需的结果：

写好＆＃34;良好的条件＆＃34;
简单地通过not条件来描述不良条件。
应用Demorgan的法律来提出正确的!=用法。

但是，我建议另一种方法是编写一个返回＆＃34; ok＆＃34;如果种子颜色好：

bool seedColorOk(const std::string& sColor)
{
   return seedColor == "red" || seedColor == "Red" || 
        seedColor == "blue" || seedColor == "Blue";
}
//...
if( !seedColorOk(seedColor))
{
   // this is a bad seed color
}
else
{
   // this is a good seed color
}

然后可以自定义该功能而不会破坏原始代码。

Answer 2

如果seedColor是＆＃34;红色＆＃34;那么seedColor！=＆＃34; Red＆＃34;将是真的。

如果seedColor是＆＃34; Red＆＃34;那么seedColor！=＆＃34;红色＆＃34;将是真的。

如果seedColor是其他任何东西，那么seedColor！=＆＃34; Red＆＃34;和seedColor！=＆＃34;红色＆＃34;两者都是真的。

所以无论seedColor是什么，表达式seedColor！=＆＃34; red＆＃34; || seedColor！=＆＃34; Red＆＃34;将是真的。想想你应该如何结合两个子表达式来获得你想要的东西。

如前所述，＆amp;＆amp;优先级高于||，因此需要修复另一个问题。

Answer 3

问题主要不在于！=关闭。在此学习逻辑运算符的优先级：http://www.learncpp.com/cpp-tutorial/36-logical-operators/：D 这是“正确”的方式。（如果这是你想要的结果）

#include <iostream>
#include <string>

using namespace std;


int main ()
{
//Get Seed Color
string seedColor = "";
cout << "Enter Your Seed's Color: \n";
cin >> seedColor;
// Get Temp

if((seedColor != "red" && seedColor != "Red") && (seedColor != "blue" || seedColor != "Blue"))
{
cout << "Invalid Response. Please enter Red or Blue for the Color.\n";
return 0;
}

int temp = 0;
cout << "Enter Your Seed's Temperature: ";
cin >> temp;

 // if Red Seed
if(seedColor == "Red"|| seedColor == "red")
{


//if temp >= 75
if (temp >= 75)
{

     // Get Soil Moisutre
    string soilMoisture = "";
    cout << "Enter Your Soil's Moisture (Wet or Dry): ";
    cin >> soilMoisture;

    // Soil Dry Output Dandelion
    if (soilMoisture == "Wet" || soilMoisture == "wet" )
    {
        cout << "A Sunflower will grow!\n";
    }

    if (soilMoisture == "Dry" || soilMoisture == "dry")
    {
        cout << "A Dandelion will grow!\n";
    }
}


else
{
   // Otherwise Mushroom
   cout << "You will have a Mushroom!";
}



}
// if Blue seed
if (seedColor == "Blue" || seedColor == "blue")
{


//if temp b/t 60 && 70
if (temp >= 60 && temp <= 70)
{
    // Get Soil Moisutre
    string soilMoisture = "";
    cout << "Enter Your Soil's Moisture (Wet or Dry): ";
    cin >> soilMoisture;

    // Soil Dry Output Sunflower
    if (soilMoisture == "Dry" || soilMoisture == "dry")
    {
        cout << "A Sunflower will grow!";
    }
    // Soil Wet Output Dandelion
    if (soilMoisture == "Wet" || soilMoisture == "wet")
    {
        cout << "A Dandelion will grow! \n";
    }

}
else
{
    // Otherwise Mushroom
    cout << "You will have a Mushroom! \n";
}


}
    return 0;
}

代码不工作（尝试使用！=正确）

3 个答案: