11.3

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

11.4

#include
     
      #include
      
       using namespace std;int main(){    char ch;    ifstream test1("test.txt");    while(test1.get(ch))    cout<
      
     

11.7

#include 
     
      using namespace ::std;int main(){ios_base::fmtflags original_flags = cout.flags();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); }