[Valmont]

#include <iostream>
#include <fstream>

//--
using std::cin;
using std::ifstream;
using std::ofstream;
using std::cout;
using std::endl;
//--

int main()
{
  float test_data[4];
  test_data[0] = 1.23;
  test_data[1] = 2.34;
  test_data[2] = 3.45;
  test_data[3] = 4.56;

  //**** OUTPUT TEST_DATA ****
  ofstream outfile("test.txt", std::ios::out);
  for(short i=0; i<4; i++)
  {
    outfile <<  test_data[i] << "  ";
    outfile << endl;
  }
  outfile.close();


  //**** INPUT TEST_DATA TO SAMPLE ****

  float sample[4] = {0};  //Always good to intialize arrays.
  short i(0);
  ifstream infile("test.txt", std::ios::in);
  while(infile >> sample[i])
  {
    ++i;
  }
  infile.close();
  
  //Test
  for(short i=0; i < 4; ++i)
  {
    cout<<sample[i]<<endl;
  }

  return 0;
}

There's a lot of info on streams on this forum. Just use the "search" button. There are some pretty nice things to be found.