C++实验7

1.11.7

#include<iostream>
using namespace std;
int main(){
    ios_base::fmtflags original_flags=cout.flags();//保留现在的格式化参数设置，以便恢复 
    cout<<812<<'|';
    cout.setf(ios_base::left,ios_base::adjustfield);//左对齐 
    cout.width(10);//指定输出宽度为10 
    cout<<813<<815<<'\n';
    cout.unsetf(ios_base::adjustfield);//取消对齐方式 
    cout.precision(2);
    cout.setf(ios_base::uppercase|ios_base::scientific);//对于科学格式显示大写字母E，以科学格式显示浮点数值 
    cout<<831.0;
    cout.flags(original_flags);//恢复原来的参数设置 
    return 0;
}

2.11.3.4

#include<fstream>
using namespace std;
int main(){
    ofstream myFile("test1.txt");
    myFile<<"已成功写入文件！";
    myFile.close();
    return 0;
} 

#include<iostream>
#include<fstream>
#include<cstring>
using namespace std;
int main(){
    string s;
    ifstream in("test1.txt");
    if(!in){
        cout<<"fail to open." << endl;
        return 1;
    }
    in>>s;
    cout<<s<<endl;
    in.close();
    return 0;
}

3.

#include<iostream>
#include<cstring>
#include<fstream>
#include<cstdlib>
#include<ctime>
using namespace std;
struct student
{
    string num;
    string id,name,cls;
}stu[100];
int main()
{    
    ifstream fin("list.txt");
    ofstream fout("roll.txt");
    if(!fin)
    {
        cout<<"ÎÞ·¨´ò¿ªÎļþ"<<endl;
        return 1; 
    }
    int i=0;
    while(fin>>stu[i].num>>stu[i].id>>stu[i].name>>stu[i].cls)
    {i++;}
    fin.close();
    int line=i;
    int t;
    srand(time(NULL));
    for(int i=0;i<5;i++)
    {
        t=rand()%line+1;
        cout<<stu[t].num<<" "<<stu[t].id<<" "<<stu[t].name<<" "<<stu[t].cls<<endl;
        fout<<stu[t].num<<" "<<stu[t].id<<" "<<stu[t].name<<" "<<stu[t].cls<<endl;
    }
    fout.close();
    return 0;
}