如何如果用户输入匹配特定值？

  • Z时代
  • 2024-01-10
  • 分类：问答

我正在写一个简单的C++测量程序，要求用户输入来选择他们想从哪个单位测量单位和单位？但我不知道结构是否正确（我的C++真的很糟糕）。这里是我的代码：如何如果用户输入匹配特定值？

#include <iostream> 
using namespace std; 
int main() 
{ 
    int storeFROM, storeTO; 
    char mm, cm, m, kk; 
    cout << "Enter the initial unit (mm, cm, m, or km): "; 
    cin >> storeFROM; 
    cout << endl; 
    if ((storeFROM != 'mm') || storeFROM != 'cm' || storeFROM != 'm' || storeFROM != 'km') { 
     cout << "--> Sorry unit to convert FROM is invalid" << endl; 
    } 
    else if ((storeFROM == 'mm') || storeFROM == 'cm' || storeFROM == 'm' || storeFROM == 'km') 
    { 
     cout << "Enter the initial unit(mm, cm, m, or kk) :"; 
     cin >> storeTO; 
    } 
    // Calculate the selected units 
    system("pause"); 
}

我希望有人能帮助我，要求用户填写他们想哪个单位来问，这正是它应该如何显示：

回答：

下面是正确的代码：

bool isValidUnit(const std::string &unit); 
int convertValue(double value, const std::string &unitFrom, const std::string &unitTo); 
int main() { 
    ... 
    std::string storeFROM, storeTO; 
    cout << "Enter the initial unit (mm, cm, m, or km): "; 
    cin >> storeFROM; 
    if (!isValidUnit(storeFROM)) { 
     cout << "--> Sorry unit to convert FROM is invalid" << endl; 
     ... 
    } 
    cout << "Enter the initial unit (mm, cm, m, or km): "; 
    cin >> storeTO; 
    if (!isValidUnit(storeTO)) { 
     cout << "--> Sorry unit to convert TO is invalid" << endl; 
     ... 
    } 
    double value; 
    cout << "Enter the value in (" << storeFROM << "): "; 
    cin >> value; 
    double valueConverted = convertValue(value, storeFROM, storeTO); 
    cout << "Value in (" << storeTO << "): " << valueConverted << endl; 
    return 0; 
} 
bool isValidUnit(const std::string &unit) { 
    return unit == "mm" || unit == "cm" || unit == "m" || unit == "km"; 
} 
double unitMultiplier(const std::string &unit) { 
    if (unit == "mm") return 0.001; 
    if (unit == "cm") return 0.01; 
    if (unit == "m") return 1; 
    if (unit == "km") return 1000; 
    return 0.; 
} 
double convertValue(double value, const std::string &unitFrom, const std::string &unitTo) { 
    if (unitFrom == unitTo) return value; 
    if (value <= 0.) return 0.; // or value :) 
    // Get it in meters 
    int valueInMetes = value * unitMultiplier(unitFrom); 
    return valuesInMeter/unitMultiplier(unitTo); 
}

回答：

在程序，storeFROM和storeTO都是string S，所以你应该把他们定义为string S：

string storeFROM, storeTO;

当将它们与"cm","mm"等值进行比较时，您应该在""中引用它们，而不是''，因为您绝对不希望它们是multicharacter literals。它应该是这样的：

if ((storeFROM != "mm") || storeFROM != "cm" 
         || storeFROM != "m" || storeFROM != "km") 
{ 
    cout << "--> Sorry unit to convert FROM is invalid" << endl; 
} 
else if ((storeFROM == "mm") || storeFROM == "cm" 
          || storeFROM == "m" || storeFROM == "km") 
{ 
    cout << "Enter the initial unit(mm, cm, m, or kk) :"; 
    cin >> storeTO; 
}

回答：

string storeFROM, storeTO; // note string thingie 
float value1, value2; 
cin>>storeFROM; 
if ((storeFROM != "mm") || storeFROM != "cm" || storeFROM != "m" || storeFROM != "km")) 
{ 
    cout << "--> Sorry unit to convert FROM is invalid" << endl; 
} 
else 
{ 
    cin>>value1; 
    cout << "Enter the initial unit(mm, cm, m, or kk) :"; 
    cin >> storeTO; 
    if((storeTO == "mm") || storeTO == "cm" || storeTO == "m" || storeTO == "km")) 
    { 
     cin>>value2; 
      //convert here... 
      //hint: use switch-case 
    } 
} 
//end programme

这里...

回答：

您不能输入非接受的符号，例如字母'm'表示int类型的对象。

您可以将此代码用作程序的模板。

#include <iostream> 
#include <string> 
#include <initializer_list> 
#include <algorithm> 
#include <cstdlib> 
std::ostream & display_meazures(const std::initializer_list<const char *> &l, 
           std::ostream &os = std::cout) 
{ 
    auto it = l.begin(); 
    for (size_t i = 0; i < l.size(); i++) 
    { 
     if (i == l.size() - 1) os << "or "; 
     os << *it; 
     if (i != l.size() - 1) os << ", "; 
    } 
    return os; 
} 
int main() 
{ 
    std::string storeFROM, storeTO; 
    std::initializer_list<const char *> meazure = { "mm", "cm", "m", "km" }; 
    while (true) 
    { 
     std::cout << "Enter the initial unit (" << display_meazures(meazure) 
       << "): "; 
     std::cin >> storeFROM; 
     if (std::find(meazure.begin(), meazure.end(), storeFROM) != 
      meazure.end()) 
     { 
     break; 
     } 
     std::cout << "--> Sorry unit to convert FROM is invalid" << std::endl; 
     std::cout << std::endl; 
    } 
// Calculate the selected units 
    std::system("pause"); 
}

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