11-7

#include
     
      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);//把对齐方式转为左对齐    cout.width(10);//把输出域的宽度由0改为10    cout << 813 << 815 << '\n';    cout.unsetf(ios_base::adjustfield);//消除对齐方式的设置     cout.precision(2);//设置精度2    cout.setf(ios_base::uppercase | ios_base::scientific);//更改浮点数的显示设置     cout << 831.0;    cout.flags(original_flags);//恢复初始参数    return 0;}
     

11-3

#include
     
        #include
      
       using namespace std;int main() {    ofstream s("d://text.txt");    s << "已成功写入文件!" << endl;    s.close();    return 0;}
      
     

11-4

#include 
     
      #include
      
       using namespace std;int main(){    ifstream s("test1.txt");    char ch;    while((ch=s.get())!=EOF)        cout.put(ch);    s.close();    return 0;}
      
     

1

#include
     
      #include
      
       #include
       
        #include
        
         #include
         
          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<<"无法打开文件"<
          
           >stu[i].num>>stu[i].id>>stu[i].name>>stu[i].cls) { i++; }　　 fin.close(); int line=i; int a; srand(time(NULL)); for(int i=0;i<5;i++) { a=rand()%line+1; cout<
           
            <<" "<
            
             <<" "<
             
              <<" "<
              
               <