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[题目] 设计一个学生学籍管理系统 学生信息包括：姓名、学号、性别和英语、数学、程序设计、体育成绩。 从键盘输入数据，建立数据文件student.dat。 实现对学生或学号查询，显示信息。 对所有学生，按照班级计算平均成绩。 分别按照英语、数学、程序设计和体育成绩排序生成结果文件。 [设计]建立student类存储学生信息，并通过vector输入学生数据、输出到文件、从文件读入学生数据，再进行下一步操作
源码：
#include <iostream>#include <algorithm>#include <string>#include <fstream>#include <vector>#include <string>using namespace std;bool optNext();//定义student类，存储学生信息class student{public://构造函数student(fstream &);student(string, long, string, int, int, int, int){this->name = name;this->stuID = stuID;this->sex = sex;this->enSc = enSc;this->maSc = maSc;this->peSc = peSc;this->prSc = prSc;}//获取学生信息//通过public类型函数访问private类型的学生数据int getEn(){return enSc;}int getMa(){return maSc;}int getPr(){return prSc;}int getPe(){return peSc;}//定义操作类friend bool disbyID(long);friend bool disbyName(string &);friend bool add();friend bool avgSc();friend bool resSc();friend bool readFile(fstream &infile);friend bool saveFile(ofstream &);private://定义学生属性string name;long stuID;string sex;int enSc;int maSc;int prSc;int peSc;};//存放学生信息，遍历学生信息vector<student> vec;vector<student>::iterator it;bool readFile(fstream &infile){while (!infile.eof()){vec.push_back(infile);infile.get();}return true;}student::student(fstream &infile) {infile >> name;infile >> stuID;infile >> sex;infile >> enSc;infile >> maSc;infile >> prSc;infile >> peSc;}bool saveFile(ofstream &outfile){bool emptyCheck = true; //标志文件为空it = vec.begin();while (it != vec.end()){if (!emptyCheck) //读入文件outfile << endl; //如果是空文件则不添加回车符，否则先添加回车符再输出下一条学生数据outfile << it->name << " " << it->stuID << " " << it->sex<< " " << it->enSc << " " << it->maSc << " " << it->prSc << " " << it->peSc;it++;emptyCheck = false; //标志文件不为空}return true;}//通过学号查找学生数据bool disbyID(long id){it = vec.begin();do{if (it->stuID == id) //如果找到了学号符合的学生数据则输出并结束查找{cout << it->name << " " << it->stuID << " " << it->sex << " " << it->enSc << " " << it->maSc << " " << it->prSc << " " << it->peSc << endl;break;}else it++;} while (it != vec.end());if (it == vec.end()) //如果查到最后一条数据也没有找到符合的学生则输出错误信息{cout << "没有找到符合的学生ID!" << endl;}return true;}//通过学生姓名查找学生数据bool disbyName(string &name){it = vec.begin();do{if (it->name == name) //如果找到了姓名符合的学生数据则输出并结束查找{cout << it->name << " " << it->stuID << " " << it->sex << " " << it->enSc << " " << it->maSc << " " << it->prSc << " " << it->peSc << endl;break;}else it++;} while (it != vec.end());if (it == vec.end()) //如果查到最后一条数据也没有找到符合的学生则输出错误信息{cout << "没有找到符合的学生姓名!" << endl;}return true;}//添加一条新的学生数据bool add(){string name;long stuID;string sex;int enSc;int maSc;int peSc;int prSc;cout << "请输入学生信息: " << endl;cout << "name: ";cin >> name;cout << "学生 ID: ";cin >> stuID;cout << "学生 性别[男/女]: ";cin >> sex;cout << "学生英语成绩: ";cin >> enSc;cout << "学生数学成绩: ";cin >> maSc;cout << "学生程序设计成绩: ";cin >> prSc;cout << "学生体育成绩: ";cin >> peSc;//将新添加的学生数据压栈入vectorvec.push_back(student(name, stuID, sex, enSc, maSc, prSc, peSc));return true;}//计算学生每一门平均成绩bool avgSc(){int i;float sumEn = 0, avgEn = 0;float sumMa = 0, avgMa = 0;float sumPr = 0, avgPr = 0;float sumPe = 0, avgPe = 0;it = vec.begin();for (i = 0; it != vec.end(); it++, i++){sumEn += (float)it->enSc;sumMa += (float)it->maSc;sumPr += (float)it->prSc;sumPe += (float)it->peSc;}avgEn = sumEn / (float)i;avgMa = sumMa / (float)i;avgPr = sumPr / (float)i;avgPe = sumPe / (float)i;cout << "英语: " << avgEn << " 数学: " << avgMa << " 程序设计: " << avgPr << " 体育: " << avgPe << endl;return true;}//按照各门成绩排序方法bool cmpEnglish(student a, student b){return a.getEn()>b.getEn();}bool cmpMath(student a, student b){return a.getMa()>b.getMa();}bool cmpProgramming(student a, student b){return a.getPr()>b.getPr();}bool cmpPE(student a, student b){return a.getPe()>b.getPe();}//按各门成绩排序并输出文件bool resSc(){ofstream outfile_en("English.dat", ios::out); //打开English.dat文件并建立输入流if (!outfile_en){cout << "open error!" << endl; //打开失败则报错exit(1);}sort(vec.begin(), vec.end(), cmpEnglish); //按照英语成绩排序vector<student>::iterator iter_en;for (iter_en = vec.begin(); iter_en != vec.end(); iter_en++) //输出到文件{outfile_en << iter_en->name << " " << iter_en->stuID << " " << iter_en->sex << " " << iter_en->enSc << " " << iter_en->maSc << " " << iter_en->prSc << " " << iter_en->peSc << endl;}outfile_en.close(); //关闭输入流ofstream outfile_ma("Math.dat", ios::out);if (!outfile_ma){cout << "open error!" << endl;exit(1);}sort(vec.begin(), vec.end(), cmpMath);vector<student>::iterator iter_ma;for (iter_ma = vec.begin(); iter_ma != vec.end(); iter_ma++){outfile_ma << iter_ma->name << " " << iter_ma->stuID << " " << iter_ma->sex << " " << iter_ma->enSc << " " << iter_ma->maSc << " " << iter_ma->prSc << " " << iter_ma->peSc << endl;}outfile_ma.close();ofstream outfile_pro("Program.dat", ios::out);if (!outfile_pro){cout << "open error!" << endl;exit(1);}sort(vec.begin(), vec.end(), cmpProgramming);vector<student>::iterator iter_pr;for (iter_pr = vec.begin(); iter_pr != vec.end(); iter_pr++){outfile_pro << iter_pr->name << " " << iter_pr->stuID << " " << iter_pr->sex << " " << iter_pr->enSc << " " << iter_pr->maSc << " " << iter_pr->prSc << " " << iter_pr->peSc << endl;}outfile_pro.close();ofstream outfile_pe("PE.dat", ios::out);if (!outfile_pe){cerr << "open error!" << endl;exit(1);}sort(vec.begin(), vec.end(), cmpPE);vector<student>::iterator iter_pe;for (iter_pe = vec.begin(); iter_pe != vec.end(); iter_pe++){outfile_pe << iter_pe->name << " " << iter_pe->stuID << " " << iter_pe->sex << " " << iter_pe->enSc << " " << iter_pe->maSc << " " << iter_pe->prSc << " " << iter_pe->peSc << endl;}outfile_pe.close();cout << "output succeed!" << endl;return true;}bool optNext(){string opt2;int exit_ck = 1;while (exit_ck) {//循环结构，在选择每个选项后再次执行这一步cout << "A:查询学生ID" << endl;cout << "B:查询学生姓名" << endl;cout << "C:统计平均成绩" << endl;cout << "D:成绩保存到文件" << endl;cout << "X:退出" << endl;cin >> opt2;if (opt2 == "A") {long sID;cout << "请输入学生ID: " << endl;cin >> sID;disbyID(sID);}if (opt2 == "B") {string sName;cout << "请输入学生姓名: " << endl;cin >> sName;disbyName(sName);}if (opt2 == "C"){avgSc();}if (opt2 == "D"){resSc();}if (opt2 == "X") //标记退出符号，在下次循环开始时退出exit_ck = 0;}return true;}int main(){string opt1;cout << "A:读取学生信息" << endl;cout << "B:新建学生信息" << endl;cin >> opt1;if (opt1 == "A") //read from existed file{cout << "输入学生信息读取文件: " << endl;string fileName1;cin >> fileName1;fstream infile(fileName1);if (!infile) {cout << "文件打开失败!" << endl;exit(0);}readFile(infile);optNext();}else if (opt1 == "B"){//enter new student datacout << "请输入添加的学生数量: " << endl;int n;cin >> n;for (int i = 0; i < n; ++i)add();cout << "信息添加成功，请输入保存的文件名: ";string fileName2;cin >> fileName2;ofstream outFile(fileName2, fstream::trunc | fstream::out);cout << "保存中......" << endl;saveFile(outFile);cout << "保存成功!" << endl;outFile.close();optNext();}return 0;}
[小结]
在第一次建立输出到文件的函数时，没有考虑到回车符和eof，导致在最后一条数据输出到文件后多数出了一个回车符，在下次读入时会多读入一条空数据，解决方案是加入一个bool标记标志文件是否为空，当文件为空时不输出回车符，否则先输出回车符再输出下一条学生数据。
[运行结果]
系统截图如下：
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