functions.php

<?php

function list_option($arr){
  $choice = '';
  while(list($k,$v)=each($arr))
  {
    $choice.='<option value = "'.$k.'">'.$k.'</option>';
  }
}
 // defines array of length and area
 // acres and hectares are squared due to function parameters
define('LENGTH_TO_METER',array(
    "inches" => 0.0254,
    "feet" => 0.3048,
    "yards" => 0.9144,
    "miles" => 1609.344,
    "millimeters" => 0.001,
    "centimeters" => 0.01,
    "meters" => 1,
    "kilometers" => 1000,
    "acres" => 63.614907234075,
    "hectares" => 100
  ));

define('VOLUME_TO_LITER' ,array(
    "cubic_inches" => 0.0163871,
    "cubic_feet" => 28.3168,
    "cubic_centimeters" => 0.001,
    "cubic_meters" => 1000,
    "imperial_gallons" => 4.54609,
    "imperial_quarts" => 1.13652,
    "imperial_pints" => 0.568261,
    "imperial_cups" => 0.284131,
    "imperial_ounces" => 0.0284131,
    "imperial_tablespoons" => 0.0177582,
    "imperial_teaspoons" => 0.00591939,
    "us_gallons" => 3.78541,
    "us_quarts" => 0.946353,
    "us_pints" => 0.473176,
    "us_cups" => 0.24,
    "us_ounces" => 0.0295735,
    "us_tablespoons" => 0.0147868,
    "us_teaspoons" => 0.00492892,
    "liters" => 1,
    "milliliters" => 0.001,
    ));

const MASS_TO_KILOGRAM = array(
  "ounces" =>	0.0283495,
  "pounds" =>	0.453592,
  "stones" =>	6.35029,
  "long_tons" =>	1016.05,
  "short_tons" =>	907.185,
  "milligrams" =>	0.000001,
  "grams" =>	0.001,
  "kilograms" =>	1,
  "metric_tonnes" =>	1000
);
// The function float_to_string formats a float into a string 
// while also avoiding default use of scientific notation.
// Rounds to $precision and trims extra trailing zeros.
function float_to_string($float, $precision=10) {
  // Typecast to insure value is a float
  $float = (float) $float;
  $string = number_format($float, $precision, '.', '');
  $string = rtrim($string, '0');
  $string = rtrim($string, '.');
  return $string;
}
// Length
// Convert every value to meters
function convert_to_meters($value, $from_unit) {
  if(array_key_exists($from_unit, LENGTH_TO_METER)) {
    return $value * LENGTH_TO_METER[$from_unit];
  } 
  else {
    return "Unsupported unit.";
  }
}

function convert_from_meters($value, $to_unit) {
  if(array_key_exists($to_unit, LENGTH_TO_METER)) {
    return $value / LENGTH_TO_METER[$to_unit];
  } 
  else {
    return "Unsupported unit.";
    }
}

function convert_length($value, $from_unit, $to_unit) {
    $meter_value = convert_to_meters($value, $from_unit);
    $new_value = convert_from_meters($meter_value, $to_unit);
    return $new_value;
}
/*
class Length {
  var $value;
  var $from_unit;
  var $to_unit;
  function convert_to_meters($value, $from_unit) {
    if(array_key_exists($from_unit, LENGTH_TO_METER)) {
      return $value * LENGTH_TO_METER[$from_unit];
    } 
    else {
      return "Unsupported unit.";
    }
  }
    
  function convert_from_meters($value, $to_unit) {
    if(array_key_exists($to_unit, LENGTH_TO_METER)) {
      return $value / LENGTH_TO_METER[$to_unit];
    } 
    else {
      return "Unsupported unit.";
      }
  }
    
  function convert_length($value, $from_unit, $to_unit) {
      $meter_value = convert_to_meters($value, $from_unit);
      $new_value = convert_from_meters($meter_value, $to_unit);
      return $new_value;
  }
  

}
*/
//Area

function convert_to_square_meters($value, $from_unit) {
    $from_unit = str_replace('square_', '', $from_unit);
    if(array_key_exists($from_unit, LENGTH_TO_METER)) {
      return $value * pow(LENGTH_TO_METER[$from_unit], 2);
    } else {
      return "Unsupported unit.";
    }
  }
    
function convert_from_square_meters($value, $to_unit) {
    $to_unit = str_replace('square_', '', $to_unit);
    if(array_key_exists($to_unit, LENGTH_TO_METER)) {
      return $value / pow(LENGTH_TO_METER[$to_unit], 2);
    } else {
      return "Unsupported unit.";
    }
  }
  
function convert_area($value, $from_unit, $to_unit) {
    $meter_value = convert_to_square_meters($value, $from_unit);
    $new_value = convert_from_square_meters($meter_value, $to_unit);
    return $new_value;
  }
  
//Volume
function convert_to_liters($value, $from_unit) {
    if(array_key_exists($from_unit, VOLUME_TO_LITER)) {
        return $value * VOLUME_TO_LITER[$from_unit];
    } else {
        return "Unsupported unit.";
    }
}
function convert_from_liters($value, $to_unit) {
    if(array_key_exists($to_unit, VOLUME_TO_LITER)) {
        return $value / VOLUME_TO_LITER[$to_unit];
    } else {
        return "Unsupported unit.";
    }
}
function convert_volume($value, $from_unit, $to_unit) {
    $liter_value = convert_to_liters($value, $from_unit);
    $new_value = convert_from_liters($liter_value, $to_unit);
    return $new_value;
}
// Mass
function convert_to_kilograms($value, $from_unit) {
  if(array_key_exists($from_unit, MASS_TO_KILOGRAM)) {
    return $value * MASS_TO_KILOGRAM[$from_unit];
  } else {
    return "Unsupported unit.";
  }
}
  
function convert_from_kilograms($value, $to_unit) {
  if(array_key_exists($to_unit, MASS_TO_KILOGRAM)) {
    return $value / MASS_TO_KILOGRAM[$to_unit];
  } else {
    return "Unsupported unit.";
  }
}

function convert_mass($value, $from_unit, $to_unit) {
  $liter_value = convert_to_kilograms($value, $from_unit);
  $new_value = convert_from_kilograms($liter_value, $to_unit);
  return $new_value;
}
//speed

function convert_speed($value,$from_unit,$to_unit){
    list($from_dist,$from_time)=explode ('_per_',$from_unit);
    list($to_dist,$to_time)=explode ('_per_',$to_unit);
    if ($from_time == 'hour'){ $value /= 3600;}
    $value = convert_length($value,$from_dist,$to_dist);
    if ($to_time == 'hour'){ $value /= 3600;}
    return $value;

}
//Temperature
function convert_from_celsius($value,$from_unit){
   switch($from_unit){
    case 'celsius':
        return $value;
        break;
    case 'fahrenheit':
        return ($value-32)/1.8;
        break;
    case 'kelvin':
        return $value -273.15;
        break;
    default:
        return "Unsupported unit.";
   }
}
function convert_to_celsius($value,$to_unit){
   switch($to_unit){
    case 'celsius':
        return $value;
        break;
    case 'fahrenheit':
        return ($value * 1.8 ) +32;
        break;
    case 'kelvin':
        return $value + 273.15;
        break;
    default:
        return "Unsupported unit.";
   }
}
function convert_temp($value,$from_unit,$to_unit){
  $celsius_value = convert_from_celsius($value, $from_unit);
  $new_value = convert_to_celsius($celsius_value, $to_unit);
  return $new_value;
}
function optionize($string){
    return str_replace(' ','_',strtolower($string));
    
}