[Ilugc] read and count only limited characters using php script

[Mahalingam Subramaniam]

Hi All
the aim is to read and count only 100 characters from input text file containing characters of A, G, C, T....of 500 or more.... The PHP script which I appended here reads all the 500 or whatever is present in the input file. The help which I expect from the forum is to find and correct the mistake by which it can read and count only the limited number of characters to be set as a condition.
<?php
$file="co3.txt";
$handle=fopen($file, 'r');
$A=0;
$G=0;
$C=0;
$T=0;
$contents[] = '';
    while(!feof($handle)) {
   $contents[] = fread($handle, 100);
}
#echo($contents);
 { $readchar=fgetc($handle);
  $readchar=strtoupper($readchar);
for ($i=0; $i<100; $i++)
{
#echo ($contents[$i]);
if($contents[$i] == 'A' )    # && ($A++ <=100))
 {
 
    $A++;
#   if ( $A++ <= 100 ) {
    imagefilledrectangle($img, $x1, $y1, $x2, $y2, $green);
/***to draw an image of thin vertical rectangular line for every characters read and counted which is secondary***/
    $x1=$x1+6;
    $x2=$x2+6;
}
    else
    if ($contents[$i] == 'G' )  # ($G++ <=100))
{
    $G++;
#   if ( $G++ <= 100 ) {
    imagefilledrectangle($img, $x1, $y1, $x2, $y2, $black);
    $x1=$x1+6;
    $x2=$x2+6;
}
    else
    if ($contents[$i] == 'C' )  #($C++ <=100))
{
    
    $C++;
#   if ( $C++ <= 100 ) {
    imagefilledrectangle($img, $x1, $y1, $x2, $y2, $blue);
    $x1=$x1+6;
    $x2=$x2+6;
}
    else
    if ($contents[$i] == 'T' )  #($T++ <=100))
{
    $T++;
#   if ( $T++ <= 100 ) {
    imagefilledrectangle($img, $x1, $y1, $x2, $y2, $red);
    $x1=$x1+6;
    $x2=$x2+6;
}
}
fclose($handle);
?>
I shall appreciate and honor your help.
with thanks & regards
s.mahalingam