C++ how to use cout output hex oct dec solution

#include <iostream.h>
#include <iomanip.H>
main(void)
{
       long n = 10000;
       cout << hex << n ;
       return 0;
}

#include <iostream.h>
#include <iomanip.H>
main(void)
{
       long n = 10000;
       cout << oct << n ;
       return 0;
}

#include <iostream.h>
#include <iomanip.H>
main(void)
{
       long n = 10000;
       cout << dec << n << endl;
       return 0;
}

#include <iostream>
using namespace std;

int main()
{
  cout.setf(ios::hex, ios::basefield);

  cout << 100; // this displays 64

  return 0;
}

#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
   int n;
   cout << "Enter a decimal number: ";
   cin >> n;
   cout << n << " in hexadecimal is: " 
        << hex << n << '/n'
        << dec << n << " in octal is: " 
        << oct << n << '/n'
        << setbase( 10 ) << n << " in decimal is: " 
        << n << endl;
   return 0;
}