C++ Frequency, median, and mode without using arrays

[shgu0501]

hi I'm supposed to do a frequency array and find mode,median and count, but without storing the actual data in an array. I am able to build a frequency array but I can't return the mode since I am not supposed to store the actual value in an array. Please help me with this problem.
Thank you
Guinness

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <fstream>
 
using namespace std;
 
void open_input_file(ifstream &inf);
 
int main()
{
 ifstream from_file;
 open_input_file(from_file);
 
 int i=0;
 int j=0;
 int f[30];
 int a=0;
 
 for(j=0;j<=29; j++)
 {
  f[j]=0;
 }
 
 from_file>>a;
 int mode=f[0];
 while(!from_file.eof())
 {
  i=a;
 
  f[i]=f[i]+1;
  cout<<i<<"  "<<f[i]<<"       "<<mode<<endl;
  from_file>>a;
 }
 
void open_input_file(ifstream &inf)
{
 char input_file_name[80];
 
 do
 { inf.clear();
   cout<<"Enter input file name: ";
   cin>>input_file_name;
   inf.open(input_file_name);
 } while (inf.fail());
}

[sicarie]

If you're not worried about efficiency, you can take each individual number, go through and count how many times it occurs, hold both of them aside, and then get the next, count how many times it occurs, compare it to the last. If it's larger, move the new into the old, and get the next, etc...