Program from a .dat and histogram

[unoo]

Hi,
I'm really new programming in C++ and I need your help.
I have to make a program which has to read from a .dat file a column of 9999 values (like 6548.098976) and from this file find the maximun, minimun and later on make an histogram with 90 intervals.
I have some problems because it read the data but it doesn't find the maximun and minimun, it write 57 for both.
On the other hand, I don't have any idea of how to draw an histogram. It should be something like this:
http://maps4twan.blogspot.com.es/2010/11/histogram.html

Here it's my attempt,

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

ifstream::pos_type size;
char * memblock;

int main () {
int n, i, result=memblock[0];
  ifstream file ("data.dat", ios::in|ios::binary|ios::ate);
  if (file.is_open())
  {
    size = file.tellg();
    memblock = new char [size];
    file.seekg (0, ios::beg);
    file.read (memblock, size);
    file.close();

    cout << "the complete file content is in memory";

   cout << memblock;

for (i=0;i<9999;i++)
    {
               if (memblock[i]>result) result=memblock[i];
    }
    cout<<"max numb is:"<<result;

for (n=0;n<9999;n++)
    {
               if (memblock[n]<result) result=memblock[n];
    }
    cout<<"min numb is:"<<result;
  }
  else cout << "Unable to open file";
  return 0;
}

I'm sorry for the English mistakes I may make.

[tcs]

1. Line 9: you're dereferencing an uninitialzed pointer. This could crash your program depending on the pointer variables value.
2. Line 25: you're comparing against the value received from the illegal dereferencing at line 9.
3. What kind of data does your input fike contain? May be you read in ASCII coded numbers? The decimal value 57 represents ASCII '9'