实验7

11-3

#include<iostream>
#include<fstream>
using namespace std;
int main(){
    ofstream out("test1.txt");    
    if(!out) {
        cout << "fail to open." << endl;
        return 1;
    }
     out<<"已成功写入文件！"<<endl;
     out.close();
   
    return 0;
}

 

11-4 

 

include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main() {

    string s;
    ifstream in("test1.txt");
    if(!in) {
        cout << "fail to open." << endl;
        return 1;
    }
    in >>  s;
    cout << s;
    in.close();
    return 0;
}

 

 

11-7

 #include<iostream>
using namespace std;
int main() {
    ios_base::fmtflags original_flags = cout.flags();//保存现在的格式化参数设置,以便将来恢复这些设置
    cout << 812 << '|';
    cout.setf(ios_base::left, ios_base::adjustfield);
    cout.width(10);
    cout << 813 << 815 << '\n';
    cout.unsetf(ios_base::adjustfield);
    cout.precision(2);
    cout.setf(ios_base::uppercase | ios_base::scientific); 
    cout << 831.0;
    cout.flags(original_flags);
    return 0;
}

 

 

 

 

应用练习：

（必做）

#include<iostream>
#include<fstream>
#include<string>
#include<stdlib.h>
using namespace std;
int m;
struct student
{
    string num;
    string stuid,name,cls;
}stu[100];
int main(){
    ifstream in("list.txt");
    int i=0;
    while(in>>stu[i].num>>stu[i].stuid>>stu[i].name>>stu[i].cls)
    {
        i++;
    }
    in.close();
    ofstream out("roll.txt");
    for(int i=1;i<=5;++i)
    {
        srand((unsigned)time(NULL));
        int a=rand()%a.size();
        cout<<stu[a].num<<" "<<stu[a].stuid<<" "<<stu[a].name<<" "<<stu[a].cls<<endl;
        out<<stu[a].num<<" "<<stu[a].stuid<<" "<<stu[a].name<<" "<<stu[a].cls<<endl;
    }
    out.close();
    return 0;
｝