Openning an fstream for reading/ writting (binary)

A number of options are available to the user in this program: Option 1: record entry (terminated by EOF key). Option 2: displays records. Option 3: exit program.

The user may then repeat this process. I wish to avoid overwriting records by seeking to the end of the file, and ensure that the close() and open() calls are correct.

After declaring:

fstream fs("file", ios_base::in | ios_base::out | ios_base::binary);

is it necessary to explicitly call open;

fs.open("file", ios_base::in | ios_base::binary);

if it is necessary: must binary mode be specified? and is it necessary to clear the stream prior to writing successively?

struct record
{
    char firstname[MAX], lastname[MAX];
    int score;
};

int main(){

  record r;
  // must the modes be listed in a particular order?
  fstream fs("file", ios_base::in |ios_base::out | ios_base::binary);

  if(choice == 1) // option 1 for writing 
  {
    fs.clear(); // is it necessary to clear?
    // is it necessary to explicitly call open [and close] within 'if'
    fs.open("file", ios_base::in | ios_base::binary); 
    fs.seekp(0, ios_base::end); //attempt to avoid overwriting previous records 

    fs.write( (char *)&r, sizeof(r) );
    fs.close(); // is it best to close the file here...
  } 
  else if(choice == 2){ /*Display records*/ }
  else if(choice == 3){ exit(1); }

  /* would it be incorrect to fs.close() here and not call fs.open() */

  return 0;
}