CPP Study_2005_1/STL성적처리_3_class

Describe CPPStudy_2005_1/STL성적처리_3_class here.
~cpp 
#include <fstream>  
#include <iostream> 
#include <string> 
#include <vector> 
#include <algorithm> //sort 
#include <numeric> //accumulate 

const int SUBJECT_NO = 4; 

using namespace std;  

class student_table
{
public:
	void readdata();//파일로부터 데이터를 읽어온다 
	void printdata(); //출력 
	void operation(); //총합과 평균 
	
	vector<student_table>::iterator zbegin() { return ztable.begin(); }
	vector<student_table>::iterator zend() { return ztable.end(); }
	double average() {return avg;}


private:
	string name;
	vector<int> score;
	unsigned int total;
	double avg;
	
	vector<student_table> ztable;
};

bool zcompare(student_table& x,student_table& y);  //sort시 비교 조건 

 
int main()  
{  
 
	student_table z;
	
	//자료를 읽는다. 
	z.readdata();
	
	//총점과 평균 
	z.operation(); 

	//평균으로 정렬 
	sort(z.zbegin(),z.zend(),zcompare); 
 
	//출력 
	z.printdata(); 

	return 0;  
	
}  
 
 
 
//파일로부터 데이터를 읽어온다 
void student_table::readdata(){ 
         
	ifstream fin("data.txt"); 
	student_table tmp; 
	int tmp2,i; 

	while(1) 
	{ 
		fin >> tmp.name; 

		for(i=1;i<=SUBJECT_NO;i++) 
		{ 
			fin >> tmp2; 
			tmp.score.push_back(tmp2); 
		} 
     

		if(fin.eof()) break; 
		ztable.push_back(tmp); 
	} 
 
} 
 
//sort시 비교 조건 
bool zcompare(student_table& x,student_table& y) 
{        
        return x.average() > y.average(); 
} 

//출력하기 
void student_table::printdata() 
{ 
    int cnt=0; 
    cout << "이름\t국어\t영어\t수학\t과학\t총점\t평균" << endl; 
    for(vector<student_table>::iterator i=ztable.begin();i<ztable.end();++i) 
    { 
         
        cout << i->name << "\t" << 
                i->score[cnt*4+0] << "\t" <<  
                i->score[cnt*4+1] << "\t" << 
                i->score[cnt*4+2] << "\t" << 
                i->score[cnt*4+3] << "\t" <<  
                i->total << "\t" << 
                i->avg <<endl; 
        cnt++; 
         
    } 

 
} 
 
void student_table::operation() 
{ 
    for(vector<student_table>::iterator i=ztable.begin() ;i<ztable.end();++i) 
    { 
            i->total = accumulate(i->score.begin()+i->score.size()-4,i->score.end(),0); 
            i->avg = i->total/4.0; 
    } 

}