Max and Min of float numbers in txt file

I have problem in finding the min and max of floating numbers in txt file. The number are stored in a file as one number per line. The Programm should go through these numbers and find the biggest and smallest number.

Let say i have the following numbers(two digits after comma and four digits before):

0005.00 0005.23 52340.53 0000.01 0111.10 0001.00 2523.00

When i run it i get weird results! Any help is appreciated.

#include<fstream>
#include<cstdlib>
#include<iostream>
#include <iomanip>
using namespace std;

int main()
{
int counter=0, number;
float  sum = 0, average=0;
char file_name [20];
cout << "enter filename: ";
cin >> file_name;
ifstream input;
input.open(file_name);
if (! input)
{
cout << "Can't open file" << file_name;
//exit (0); 
 }

input  >> number;
float min = number;
float max = number;

while (input>>number)
{
counter++;
sum=sum+number;
 // Now, we can also check for Min/Max...
 if (number > max) max = number;
 if (number < min) min = number;
 }
 average=sum/counter;
 cout<< fixed<<cout.precision(3);
 cout<< "The average file in file test is was "<<average<<endl;
 cout<< fixed<<cout.precision(3);
 cout<<"The largest number is: "<<max<<endl;
 cout<< fixed<<cout.precision(3);
 cout<<"The smallest number is: "<<min<<endl;
 input.close();
 return 0;
 }

The results:

6The average file in file test is was nan

3The largest number is: 5.000

3The smallest number is: 5.000