在另一个成员函数中调用成员函数时，在“int”之前的预期主表达式

Posted 2023-02-22

【中文标题】在另一个成员函数中调用成员函数时，在“int”之前的预期主表达式

【英文标题】：Expected primary-expression before 'int' when calling a member function inside another member function

【发布时间】：2019-07-24 13:58:33

【问题描述】：

我刚开始学习 c++，我想通过做一个小项目来衡量我的理解 我正在使用类和成员函数创建一个模拟自动售货机的程序。我只收到以下 2 个错误： 'int'之前的预期主要期望

我尝试删除 int，但它给了我对变量错误的未定义引用。非常感谢任何帮助！

#include <iostream>

class DrinkMachine

  private:
    const int COST_OF_DRINK = 150;

  public:
    int RunningTotal;

    DrinkMachine()
    
      RunningTotal = 0;
    

    void DepositCoins(int money)
    

      std::cout << "You can deposit coins of values 25, 50 and 100" << std::endl;
      std::cout << "Enter a coin: " << std::endl;

      switch(money)
      
        case(25):
          RunningTotal += 25;
          break;

        case(50):
            RunningTotal += 50;
            break;

        case(100):
            RunningTotal += 100;
            break;

        default:
            std::cout << "You entered the wrong coin" << std::endl;
            std::cout << "Coins of values 25, 50, 100 are allowed" << std::endl;
            break;
      
    


    bool CheckTotal()
    
      if(RunningTotal >= COST_OF_DRINK)
        return true;

      else
        return false;
    

    void MakeDrinkSelection(int DrinkChoice)
    

      bool IsChoiceValid = false;

      while(!IsChoiceValid)
      
        switch(DrinkChoice)
        
          case (1):
            std::cout << "Thank you for choosing Coffee!" << std::endl;
            ReturnChange();
            IsChoiceValid = true;
            break;

          case(2):
            std::cout << "Thank you for choosing Hot Chocolate!" << std::endl;
            IsChoiceValid = true;
            ReturnChange();
            break;

          case(3):
            std::cout << "Thank you for choosing Green Tea!" << std::endl;
            IsChoiceValid = true;
            ReturnChange();
            break;

          default:
            std::cout << "Invalid selection. Please re-enter your choice" << std::endl;
            bool NewDrinkChoice;
            DrinkChoice = NewDrinkChoice;
            IsChoiceValid = false;
            break;
        
      
    


    void DisplayDrinks()
    
      std::cout << "----------------" << std::endl;
      std::cout << "1. Coffee" << std::endl;
      std::cout << "2. Hot Chocolate" << std::endl;
      std::cout << "3. Green Tea" << std::endl;
      std::cout << "----------------" << std::endl;
      std::cout << std::endl;
      std::cout << "Please make a choice: " << std::endl;
      MakeDrinkSelection(int DrinkChoice);  //gives an error

    

    void ReturnChange()
    
      if(RunningTotal > COST_OF_DRINK)
      
        std::cout << "Your change is: " << (RunningTotal - COST_OF_DRINK) << std::endl;
      
    
;


int main()



  //DrinkMachine drinkmachine = new DrinkMachine();
  DrinkMachine mydrink;

  while(!mydrink.CheckTotal())
  
    mydrink.DepositCoins(int money); //gives an error
  

  mydrink.DisplayDrinks();

  return 0;

【问题讨论】：

投票结束是一个错字。在main 的调用和函数中删除int money。只需在函数体中添加int money;。

@NathanOliver，这个错误出现在两个地方，这表明有一个关于如何使用参数调用函数的教训。如果要关闭它，我敢肯定那里有一个副本，至少可以将 Advait 转发给答案。

@Romen SO 不能替代一本好的参考书。我们确实希望一些已经知道的基本知识以及如何调用函数是，至少恕我直言，一个非常基本的概念。

@NathanOliver 我尝试了您的解决方案并编译了程序，但它创建了一个无限循环。还有什么我可以尝试的吗？

Error "expected primary-expression before int"的可能重复

【参考方案1】：

好吧，代码中有很多错误。我之前没有完全看到他们的程序。 我认为你可能做对了。那好吧。

首先，您应该在程序开始时询问机器可以接受哪些硬币，而您没有。

其次，在按值调用函数之前，您应该从用户那里获取输入，然后将其传递给函数，而您也没有这样做。

在这里，我已经稍微更正了您的代码。

    #include <iostream>

    class DrinkMachine
    
     private:
        const int COST_OF_DRINK = 150;

      public:
        int RunningTotal;

DrinkMachine()

  RunningTotal = 0;


void DepositCoins(int money)




  switch(money)
  
    case(25):
      RunningTotal += 25;
      break;

    case(50):
        RunningTotal += 50;
        break;

    case(100):
        RunningTotal += 100;
        break;

    default:
        std::cout << "You entered the wrong coin" << std::endl;
        std::cout << "Coins of values 25, 50, 100 are allowed" << std::endl;
        break;
  



bool CheckTotal()

  std::cout << "You can deposit coins of values 25, 50 and 100" << std::endl;
  std::cout << "Enter a coin: " << std::endl;
  if(RunningTotal >= COST_OF_DRINK)
    return true;

  else
    return false;


void MakeDrinkSelection(int DrinkChoice)


  bool IsChoiceValid = false;

  while(!IsChoiceValid)
  
    switch(DrinkChoice)
    
      case (1):
        std::cout << "Thank you for choosing Coffee!" << std::endl;
        ReturnChange();
        IsChoiceValid = true;
        break;

      case(2):
        std::cout << "Thank you for choosing Hot Chocolate!" << std::endl;
        IsChoiceValid = true;
        ReturnChange();
        break;

      case(3):
        std::cout << "Thank you for choosing Green Tea!" << std::endl;
        IsChoiceValid = true;
        ReturnChange();
        break;

      default:
        std::cout << "Invalid selection. Please re-enter your choice" << std::endl;
        bool NewDrinkChoice;
        DrinkChoice = NewDrinkChoice;
        IsChoiceValid = false;
        break;
    
  



void DisplayDrinks()

  int DrinkChoice;                //here declared
  std::cout << "----------------" << std::endl;
  std::cout << "1. Coffee" << std::endl;
  std::cout << "2. Hot Chocolate" << std::endl;
  std::cout << "3. Green Tea" << std::endl;
  std::cout << "----------------" << std::endl;
  std::cout << std::endl;
  std::cout << "Please make a choice: " << std::endl;
  std::cin>>DrinkChoice;              //input by user
  MakeDrinkSelection(DrinkChoice);  //used to give an error



void ReturnChange()

  if(RunningTotal > COST_OF_DRINK)
  
    std::cout << "Your change is: " << (RunningTotal - COST_OF_DRINK) << std::endl;
  

;


    int main()
    


  //DrinkMachine drinkmachine = new DrinkMachine();
  DrinkMachine mydrink;
  int money;              //here declared

  while(!mydrink.CheckTotal())
  
  std::cin>>money;          //input by user

    mydrink.DepositCoins(money); //no error
  

       mydrink.DisplayDrinks();

       return 0;
    

我已经清除了您询问的基本错误。但逻辑上的错误你应该自己改正。

希望你会。

【讨论】：

感谢您更正我的代码！我会尝试解决逻辑错误

欢迎，if(stuck.==true)then ask;