<"as is" basis.
# c) Use of this code, or any part thereof, is contingent upon leaving
#   this copyright notice, name and address information in tact.
# d) Written permission must be obtained from us before this code, or any
#   part thereof, is sold or used in a product which is sold.
# e) By using this code, you accept full responsibility for its use
#   and will not hold the Analysis and Solutions Company, its employees
#   or officers liable for damages of any sort.
# f) This code is not to be used for illegal purposes.
# g) Please email us any revisions made to this code.
#
# Copyright 2000         http://www.AnalysisAndSolutions.com/code/
# The Analysis and Solutions Company     info@AnalysisAndSolutions.com
# ------------------------------------------------------------------------
#
# DESCRIPTION:
# Credit Card Validation Solution uses a four step process to ensure
# credit card numbers are keyed in correctly. This procedure accurately
# checks cards from American Express, Australian BankCard, Carte Blache,
# Diners Club, Discover/Novus, JCB, MasterCard and Visa.
#
# CAUTION:
# CCVS uses exact number ranges as part of the validation process. These
# ranges are current as of 20 October 1999. If presently undefined ranges
# come into use in the future, this program will improperly deject card
# numbers in such ranges, rendering an error message entitled "Potential
# Card Type Discrepancy." If this happens while entering a card & type
# you KNOW are valid, please contact us so we can update the ranges.
#
# POTENTIAL CUSTOMIZATIONS:
# * If you don't accept some of these card types, edit Step 2, using pound
# signs "#" to comment out the "elseif," "$CardName" and "$ShouldLength"
# lines in question.
# * Additional card types can be added by inserting new "elseif,"
# "$CardName" and "$ShouldLength" lines in Step 2.
# * The three functions here can be called by other PHP documents to check
# any number.
#
# CREDITS:
# We learned of the Mod 10 Algorithm in some Perl code, entitled
# "The Validator," available on Matt's Script Archive,
# http://worldwidemart.com/scripts/readme/ccver.shtml. That code was
# written by David Paris, who based it on material Melvyn Myers reposted
# from an unknown author. Paris credits Aries Solis for tracking down the
# data underlying the algorithm. At the same time, our code bears no
# resemblance to its predecessors. CCValidationSolution was first written
# for Visual Basic, on which Allen Browne and Rico Zschau assisted.
# Neil Fraser helped prune down the OnlyNumericSolution() for Perl.
function CCValidationSolution ($Number) {
  global $CardName;
  # 1) Get rid of spaces and non-numeric characters.
  $Number = OnlyNumericSolution($Number);
  # 2) Do the first four digits fit within proper ranges"Diners Club";
    $ShouldLength = 14;
  } elseif ($NumberLeft >= 3600 and $NumberLeft <= 3699) {
    $CardName = "Diners Club";
    $ShouldLength = 14;
  } elseif ($NumberLeft >= 3800 and $NumberLeft <= 3889) {
    $CardName = "Diners Club";
    $ShouldLength = 14;
  } elseif ($NumberLeft >= 3400 and $NumberLeft <= 3499) {
    $CardName = "American Express";
    $ShouldLength = 15;
  } elseif ($NumberLeft >= 3700 and $NumberLeft <= 3799) {
    $CardName = "American Express";
    $ShouldLength = 15;
  } elseif ($NumberLeft >= 3528 and $NumberLeft <= 3589) {
    $CardName = "JCB";
    $ShouldLength = 16;
  } elseif ($NumberLeft >= 3890 and $NumberLeft <= 3899) {
    $CardName = "Carte Blache";
    $ShouldLength = 14;
  } elseif ($NumberLeft >= 4000 and $NumberLeft <= 4999) {
    $CardName = "Visa";
    if ($NumberLength > 14) {
      $ShouldLength = 16;
    } elseif ($NumberLength < 14) {
      $ShouldLength = 13;
    } else {
      echo "<br /><em>The Visa number entered, $Number, in is 14 digits long.<br />Visa cards usually have 16 digits, though some have 13.<br />Please check the number and try again.</em><br />n";
      return FALSE;
    }
  } elseif ($NumberLeft >= 5100 and $NumberLeft <= 5599) {
    $CardName = "MasterCard";
    $ShouldLength = 16;
  } elseif ($NumberLeft == 5610) {
    $CardName = "Australian BankCard";
    $ShouldLength = 16;
  } elseif ($NumberLeft == 6011) {
    $CardName = "Discover/Novus";
    $ShouldLength = 16;
  } else {
    echo "<br /><em>The first four digits of the number entered are $NumberLeft. <br />If that's correct, we don't accept that type of credit card.<br />If it's wrong, please try again.</em><br />n";
    return FALSE;
  }
  # 3) Is the number the right length"<br /><em>The $CardName number entered, $Number, is missing " . abs($Missing) . " digit(s).<br />Please check the number and try again.</em><br />n";
    } else {
      echo "<br /><em>The $CardName number entered, $Number, has $Missing too many digit(s).<br />Please check the number and try again.</em><br />n";
    }
    return FALSE;
  }
  # 4) Does the number pass the Mod 10 Algorithm Checksum"<br /><em>The $CardName number entered, $Number, is invalid.<br />Please check the number and try again.</em><br />n";
  return FALSE;
  }
}
function OnlyNumericSolution ($Number) {
  # Remove any non numeric characters.
  # Ensure number is no more than 19 characters long.
  return substr( ereg_replace( "[^0-9]", "", $Number) , 0, 19);
}
function Mod10Solution ($Number) {
  $NumberLength = strlen($Number);
  $Checksum = 0;
  # Add even digits in even length strings
  # or odd digits in odd length strings.
  for ($Location = 1 - ($NumberLength % 2); $Location < $NumberLength; $Location += 2) {
    $Checksum += substr($Number, $Location, 1);
  }
  # Analyze odd digits in even length strings
  # or even digits in odd length strings.
  for ($Location = ($NumberLength % 2); $Location < $NumberLength; $Location += 2) {
    $Digit = substr($Number, $Location, 1) * 2;
    if ($Digit < 10) {
      $Checksum += $Digit;
    } else {
      $Checksum += $Digit - 9;
    }
  }
  # Is the checksum divisible by ten"<br />The $CardName number entered, $Number, <em>is</em> valid.<br />n";
    }
  } else {
    $Number = "";
  }
  # Setup an input form. Posting it calls this page again.
  echo "<form method="post" action="$REQUEST_URI">n";
  echo "<br />Credit Card Number: <input type="text" name="Number" value="$Number">n";
  echo "<input type="Submit" name="submitr" value="Check its Validity">n";
  echo "</form><br />n";
#
# ------------ END SAMPLE USER INTERFACE SECTION -------------
?>