第十六週項目2-文件保存學生名單

問題及代碼：

/* 
*Copyright (c) 2016，煙臺大學計算機學院 
*All rights reserved. 
*文件名稱：zwj.cpp 
*作    者：張偉晶 
*完成日期：2016年6月20日 
*版 本 號：v1.0 
* 
*問題描述：用文件保存學生信息
*輸入描述： 
*程序輸出： 
*/  
#include <fstream>
#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;

//定義學生類
class Student
{
public:
    Student() {};
    ~Student();
    double get_total();
    static int get_stu_num();
    static double get_total_sum();
    friend istream& operator>>(istream &in, Student &s);  
    friend ostream& operator<<(ostream &out, Student &s); 
    bool pass();
private:
    string name;
    double cpp;
    double math;
    double english;
    double total;
    static int stu_num;  //學生人數，處理爲類的靜態成員合適
    static double total_sum; //學生總分和
};

int Student::stu_num = 0;
double Student::total_sum = 0;
Student::~Student()
{
    total_sum-=total;
    stu_num--;
}

double Student::get_total()
{
    return total;
}

int Student::get_stu_num()
{
    return stu_num;
}

double Student::get_total_sum()
{
    return total_sum;
}

istream& operator>>(istream &in, Student &s)
{
    in>>s.name>>s.cpp>>s.math>>s.english;
    s.total=s.cpp+s.math+s.english;
    Student::stu_num++;   
    Student::total_sum+=s.total;
    return in;
}

ostream &operator<<(ostream &out, Student &s)
{
    out<<s.name<<"\t";
    out<<s.cpp<<"\t";
    out<<s.math<<"\t";
    out<<s.english<<"\t";
    out<<s.total;
    return out;
}


bool Student::pass()
{
    return cpp>=60 && math>=60 && english>=60;
}

int main( )
{
    Student stud[200],t; //stud[200]爲保存數據的對象數組
    string sname;
    double total_avg;
    int i=0;

 
    ifstream infile("score.txt",ios::in);
    if(!infile)     
    {
        cerr<<"open error!"<<endl;
        exit(1);
    }
    while(!infile.eof())
    {
        infile>>stud[i++];   
    }
    infile.close();


    if(Student::get_stu_num()>0)
    {
        total_avg = Student::get_total_sum() / Student::get_stu_num();
        ofstream outfile("pass_score.txt",ios::out);
        if(!outfile)
        {
            cerr<<"open error!"<<endl;
            exit(1);
        }

        for(i=0; i<Student::get_stu_num(); i++)
        {
            if(stud[i].get_total()>total_avg&&stud[i].pass())
            {
                outfile<<stud[i]<<endl;
            }
        }
        outfile.close();
        cout<<"請到文件pass_score.dat中查看名單："<<endl;
    }
    return 0;
}

運行結果：

知識點總結：

靜態常量的定義不能在類內，必須在類外。

int Student::stu_num = 0;
double Student::total_sum = 0;