c++ - 不理解通过函数传递的 C++ 参数

Question

我是 C++ 的新手，我想了解如何通过多个函数传递变量。我知道您可以使用全局变量或参数传递。

在我的代码中，我在主函数之后定义了两个函数。我已经用原型(prototype)设置了它。我在 CodeBlocks 中收到的错误是 .error: 'studentFees' was not declared in this scope。这是有道理的，因为我没有在 123 和 124 行中实现任何内容。但我不太确定如何。我也对正确实现原型(prototype)感觉不太好。

有人能帮我解决这个问题吗？

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <fstream>
#include <string>
using namespace std;

void undergradBill(
               double finalBill = 0;
               double studentTuition,
               double studentFees,
               double studentID,
               string studentLevel,
               string studentBio,
               string studentRes,
               string studentLife,
               string studentCredit
                );
void gradBill(
               double finalBill = 0;
               double studentTuition,
               double studentFees,
               double studentID,
               string studentLevel,
               string studentBio,
               string studentRes,
               string studentLife,
               string studentCredit
              );

int main()
{
    double finalBill = 0;
    double studentTuition = 0;
    double studentFees = 0;
    double studentID = 0;
    string studentLevel = "";
    string studentBio = "";
    string studentRes = "";
    string studentLife = "";
    string studentCredit = "";

    cout << "Welcome College Student!" << endl;
    cout << "This program is designed to assist you in calculating your college tuition per semester." << endl;
    cout << endl;
    cout << "Please provide the following information:" << endl;
    cout << "   -Student ID" << endl;
    cout << "   -Graduate/Undergraduate" << endl;
    cout << "   -Residency" << endl;
    cout << "   -Major" << endl;
    cout << "   -Full Time/Part Time" << endl;
    cout << "   -Credits taken this semester" << endl;
    cout << endl;
    system("PAUSE");

    system("CLS");
    cout << "Please enter your student ID." << endl;
    cout << "Student ID: ";
    cin >> studentID;
    while(cin.fail()) {
        cout << "Error: please enter a valid entry." << endl;
        cin.clear();
        cin.ignore(256,'\n');
        cout << "Student ID :";
        cin >> studentID;
    }

    cout << endl;
    cout << "Are you a graduate or undergraduate student?" << endl;
    cout << "(G/U) :";
    cin.get();
    getline(cin, studentLevel);
    while(studentLevel != "g" && studentLevel != "G" && studentLevel != "u" && studentLevel != "U") {
        cout << "Error: please enter a valid entry." << endl;
        cout << "(G/U) :";
        getline(cin, studentLevel);
    }
    if(studentLevel == "g" || studentLevel == "G") {
        cout << endl;
        cout << "Are you apart of the biology program?" << endl;
        cout << "(Y/N) :";
        getline(cin, studentBio);
        while(studentBio != "y" && studentBio != "Y" && studentBio != "n" && studentBio != "N") {
        cout << "Error: please enter a valid entry." << endl;
        cout << "(Y/N) :";
        getline(cin, studentBio);
        }
    }

    cout << endl;
    cout << "Are you a resident or New York State?" << endl;
    cout << "(Y/N) :";
    getline(cin, studentRes);
    while(studentRes != "y" && studentRes != "Y" && studentRes != "n" && studentRes != "N") {
        cout << "Error: please enter a valid entry" << endl;
        cout << "(Y/N) :";
        getline(cin, studentRes);
    }

    cout << endl;
    cout << "Are you a full time student or a part time student?" << endl;
    cout << "(F/P) :";
    getline(cin, studentLife);
    while(studentLife != "f" && studentLife != "F" && studentLife != "p" && studentLife != "P") {
        cout << "Error: please enter a valid entry." << endl;
        cout << "(F/P) :";
        getline(cin, studentLife);
    }
    if (studentLife == "p" || studentLife == "P") {
        cout << endl;
        cout << "How many credit hours are you taking this semester?" << endl;
        cout << "Credit Hours :";
        cin >> studentCredit;
        while(cin.fail()) {
        cout << "Error: please enter a valid entry." << endl;
        cin.clear();
        cin.ignore(256,'\n');
        cout << "Credit Hours :";
        cin >> studentCredit;
        }
    }

    if(studentLevel == "u" || studentLevel == "U" || studentLife == "p" || studentLife == "P") {undergradBill();}
    else {gradBill();}

    system("CLS");
    finalBill = studentTuition + studentFees;
    cout << "Student Account: " << studentID << endl;
    cout << "Billing Total: " << finalBill << endl;
}

void undergradBill() {
    if(studentLife == "f" || studentLife == "F") {
        if(studentRes == "y" && studentRes == "Y") {
            studentTuition = 3085.00;
            studentFees = 588.50;
        }
        else {
            studentTuition = 7910.00;
            studentFees = 588.50;
        }
    }
    else {
        if(studentRes == "y" && studentRes == "Y") {
            studentTuition = 257.00;
            studentFees = studentCredit * 48.95;
        }
        else {
            studentTuition = 659.00;
            studentFees = studentCredit * 48.95;
        }
    }
}

void gradBill() {
    if(studentBio == "y" || studentBio == "Y") {
        if(studentLife == "f" || studentLife == "F") {
            if(studentRes == "y" && studentRes == "Y") {
                studentTuition = 5185.00;
                studentFees =  342.14 + 900.00;
            }
            else {
                studentTuition = 10095.00;
                studentFees = 342.14 + 900.00;
            }
        }
        else {
            if(studentRes == "y" && studentRes == "Y") {
                studentTuition = studentCredit  * 432.00;
                studentFees = (studentCredit * 28.37) + 900.00;
            }
            else {
                studentTuition = studentCredit * 841.00;
                studentFees = (studentCredit * 28.37) + 900.00;
            }
        }
    }
    else {
        if(studentLife == "f" || studentLife == "F") {
            if(studentRes == "y" && studentRes == "Y") {
                studentTuition = 5185.00;
                studentFees =  342.14;
            }
            else {
                studentTuition = 10095.00;
                studentFees = 342.14;
            }
        }
        else {
            if(studentRes == "y" && studentRes == "Y") {
                studentTuition = studentCredit  * 432.00;
                studentFees = studentCredit * 28.37;
            }
            else {
                studentTuition = studentCredit * 841.00;
                studentFees = studentCredit * 28.37;
            }
        }
    }
}

我知道这个问题很多...感谢任何可以帮助我了解如何更好地完成此操作的人!

Answer 1

问题是在 C++ 中你有函数重载，这意味着你可以有两个具有相同名称但不同签名(基本上是参数)的函数。

例如，如果你有一个函数

void undergradBill(double finalBill);

与函数不同

void undergradBill();

您已经声明(我可能会非法添加)带参数的函数声明。然后，您定义了采用无 参数的函数。由于重载，这在 C++ 中有效。

所以你的问题有很多原因:首先你有非法的函数声明，这会给你带来错误。因此，编译器没有您要调用的函数的声明。由于声明和定义不匹配的问题，您将无法调用这些函数，因为您调用的函数实际上并不存在。

当然，由于您定义的函数没有参数，使用“参数”会给您带来错误，因为函数定义中不存在这些变量。