Question

好的，所以我对此非常陌生，我正在尝试创建一个计算任意数量长途电话费用的程序。我还没有走得太远，我一直试图弄清楚如何让函数重复自己。现在我收到一个错误说

第18行在'{'标记和预期'，'或';'之前不允许使用函数定义在'{'令牌之前。

第18行是 void costCalc(int numCalls)

之后的行

到目前为止，这是我的代码：

#include<iostream>
using namespace std;

int main()
{
    // Declare and initialize all variables
       int numCalls = 0;
       int length = 0;
       int hour = 0;
       char day = ' ';
       char dest = ' ';
       double cost = 0.0;

       cout<<"Enter the number of calls: ";
       cin>>numCalls;

       void costCalc(int numCalls)
 {
        if (numCalls > 0)
        {
            cout<<"Enter length of call in minutes: ";
            cin>>length;
            costCalc(numCalls-1);
         }
}

    // Request the number of calls from the user

    // Loop for the requested number of calls:

// Request the user to give you the call length, 
// call day of week and hour of call, and call
// destination

// Instantiate and initialize a Call object 
// using either 
//   a) the 4-parameter constructor, OR 
//   b) the default constructor and each of the 
//      set member functions.

// Get the cost of the call using the calcCallCost
// function and add it to the total cost of the calls.

// Use the callMsg function to print a message about the call  

     // end loop

// Report the total cost of all the calls.

     system("pause");
     return 0;
}

Answer 1

您应该在开始新功能之前关闭主功能。

您正在尝试在main中创建嵌套函数，而C或C ++不支持该函数。

您只需在main函数开头之前复制/粘贴costCalc函数的代码。

作为附注，很久以前（1994）gcc（2.95.2）支持嵌套函数作为扩展。但它从未进入C或C ++标准。

我不确定为什么嵌套函数永远不会进入标准。它接缝很简单以支持（我们可能必须使嵌套函数内联静态，但仍然）。也许是因为它会引发一些链接器和编译单元问题。

这实际上并不是什么大问题，大多数用例都可以使用命名空间来解决。

Answer 2

这会让你继续参加演出。

    #include <iostream>
    #include <iomanip> // for setprecision(2)
    using namespace std;

    class Call {

    private: double length;

    public:
        // Instantiate and initialize a Call object 
        // using either 
        //   a) the 4-parameter constructor, OR 
        Call(double theLength) 
        {
            this->length = theLength;
        }

        //   b) the default constructor and each of the 
        //      set member functions.
        Call() { }

        void SetLength(double someLength)
        {
            this->length = someLength;
        }

        double GetLength()
        {
            return this->length;
        }
    };

    double costCalc(double costPerMinute, int length)
    {
        Call thisCall(length);
        return thisCall.GetLength()*costPerMinute;
    }

    void callMsg()
    {
        cout << "This is a message about the call" << endl;
    }

    int main()
    {
        int numCalls = 0;
        int length = 0;
        double cost = 0.0;
        double costPerMinute = 0.05;

        // Request the number of calls from the user
        cout << "Enter the number of calls: ";
        cin >> numCalls;

        // Loop for the requested number of calls:
        for (int i = 0; i < numCalls; i++) 
        {
            // Request the user to give you the call length,        
            cout << "Enter length of call " << i << " in minutes: ";
            cin >> length;

            // Get the cost of the call using the calcCallCost
            // function and add it to the total cost of the calls.
            cost += costCalc(costPerMinute, length);


            // Use the callMsg function to print a message about the call 
            callMsg();

        } // end loop


        // Report the total cost of all the calls.
        cout << "Total cost is $" << setprecision(2) << cost << endl;

        return 0;
    }

编译/运行：

g++ cost.cpp 
$ ./a.out 
Enter the number of calls: 2
Enter length of call 0 in minutes: 1
This is a message about the call
Enter length of call 1 in minutes: 2
This is a message about the call
Total cost is $0.15

创建循环函数来计算成本

2 个答案: