在C ++休息之前輸出文本

Question

我正在嘗試運行一個程序，該程序輸出一些文本行，然后在輸入“ |”時退出（或至少顯示“按任意鍵以繼續”），但是，當我運行該程序並輸入“ |”時，它很簡單說“按任意鍵繼續”。因此它不會輸出我想要的文本。

這是我嘗試達到的目標的代碼：

if(value == '|')
    {
        cout << lowest << lowest_unit << " is the lowest number.\n";
        cout << highest << highest_unit << " is the highest number. \n";    
        break;
    }

如果原因不在上述代碼中，那么這就是我程序的所有代碼：

int main()
{ 
 double value;
 double realvalue;
 double lowest = 0;
 double highest = 0; 
 string unit;
 string highest_unit;
 string lowest_unit;
 cout << "Please enter a number follow by a unit: ";

 //convert units to cm for all
 while (cin >>value>>unit)
  {
    if(unit=="cm")
    {
        realvalue = value;
    }
    else if(unit=="in")
    {
        realvalue = value*2.54;
    }
    else if(unit=="m"){
        realvalue = value*100;
    }
    else if(unit=="ft")
    {
        realvalue = value*12*2.54;
    }
    else
    {
        cout << "Your units are incorrect.\n";
        break;
    }




    if (lowest == 0 && highest == 0)
    {
      lowest = value;
      highest = value;
      lowest_unit = unit;
      highest_unit = unit;
      cout << lowest << highest_unit << " is the smallest so far.\n"
           << highest << lowest_unit <<" is the largest so far.\n";
    }
    else
    {
      if (realvalue < lowest)
      {
        lowest = value;
        lowest_unit = unit;
        cout << value << lowest_unit << " is the smallest so far.\n"
             << highest << highest_unit << " is still the highest.\n";
      }
      else
      {
        if (realvalue > highest)
        {
          highest = value;
          highest_unit = unit;
          cout << lowest << lowest_unit << " is still the lowest.\n"
               << highest << highest_unit << " is the largest so far.\n";
        }
        else
        {
          cout << lowest << lowest_unit << " is still the lowest.\n"
               << highest << highest_unit << " is still the highest.\n";
        }
      }
    }
    cout << "\nPlease enter another number: ";

    if(value == '|')
    {
        cout << lowest << lowest_unit << " is the lowest number.\n";
        cout << highest << highest_unit << " is the highest number. \n";    
        break;
    }

  }
}

（它的基本作用是比較用戶輸入的不同長度，然后確定用戶輸入的最小長度和最大長度）。

如何在顯示“按任意鍵繼續”之前（或更准確地說，在輸出時）實現輸出文本的目標？

Answer 1

value是一倍。 鍵入|時，它不會被讀取為數字，也不會設置value 。 而是應在cin中設置一個故障位。

比較value == '|' 檢查value等於ASCII字符|的數字值，恰好是124，這不是您想要的。

Answer 2

您的程序每次在循環中都需要兩個輸入。

如果要在第一個輸入處停止，則需要分兩個步驟讀取輸入。

另外，您的value是數字，而不是字符串，您不能以相同的方式讀取數字和字符串。

while (1) {
    string tmp;
    if (!(cin >> tmp)) {
        break;
    }

    if (tmp == "|") {
        break;
    }

    //convert string into double
    value = stod(tmp); //todo, check conversion was well done

    if (! (cin >> unit) ) {
        break;
    }

    // rest of code
}

Answer 3

"|" 不是可以解釋為double ，因此您應該使用std::string讀取輸入。

您的代碼應如下所示：

#include <iostream>
#include <string>
using std::cin;
using std::cout;
using std::stod;
using std::string;

int main()
{ 
  double value;
  double realvalue;
  double lowest = 0;
  double highest = 0;
  string value_str;
  string unit;
  string highest_unit;
  string lowest_unit;
  cout << "Please enter a number follow by a unit: ";

  //convert units to cm for all
  while (cin >>value_str>>unit)
  {
    if (value_str == "|") // use string literal, not character constant
    {
       cout << lowest << lowest_unit << " is the lowest number.\n";
       cout << highest << highest_unit << " is the highest number. \n";
       break;
    }
    value = stod(value_str);

    // do works with value and unit
    cout << value << "\t" << unit << "\n";
  }
}