Question

我正在尝试运行一个程序，输出一些文本行然后退出（或者至少显示“按任意键继续”）当你输入“|”。但是，当我运行这个程序并输入'|' ，它只是说“按任意键继续”。所以它不会输出我想要的文本。

这是我试图实现目标的代码：

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

如果原因不在上面的代码中，那么这就是我程序的所有代码：

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;
    }

  }
}

（它基本上做的是比较用户输入的不同长度，然后决定哪个长度最小，哪个长度是用户输入的最大长度）。

如何实现我之前输出文本的目标（或更准确地说，同时）“按任意键继续”？

Answer 1

value是双倍的。当您输入|时，它不会被读作数字，并且value不会被设置。相反，应在cin中设置失败位。

比较value == '|'检查以查看value是否等于ASCII字符的数值|，恰好是124，这不是你想要的。

Answer 2

您的程序在循环中每次都需要两个输入。

如果要在第一个输入处停止，则需要分两步读取输入。

此外，您的value是一个数字，而不是字符串，您无法以相同的方式读取数字和字符串。

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

"|"不能解释为double，因此您应该使用std::string来阅读输入。

您的代码应该是这样的：

#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";
  }
}

在C ++中断之前输出文本

3 个答案: