Add api and usage page

conversions.php

@@ -1,6 +1,7 @@
 <?php
 
 function hex_to_decimal(string $hex) : int {
+    $hex = sanitize_string_input($hex);
     $chars = array(0 => 0, 1 => 1, 2 => 2, 3 => 3, 4 => 4, 5 => 5, 6 => 6, 7 => 7, 8 => 8,
         9 => 9, "A" => 10, "B" => 11, "C" => 12, "D" => 13, "E" => 14, "F" => 15);
     $decimal = 0;
@@ -13,11 +14,13 @@ function hex_to_decimal(string $hex) : int {
 }
 
 function hex_to_binary(string $hex) : int {
+    $hex = sanitize_string_input($hex);
     $decimal = hex_to_decimal($hex);
     return decimal_to_binary($decimal);
 }
 
 function decimal_to_hex(int $decimal) : string {
+    $decimal = sanitize_int_input($decimal);
     $chars = array(0 => 0, 1 => 1, 2 => 2, 3 => 3, 4 => 4, 5 => 5, 6 => 6, 7 => 7, 8 => 8,
         9 => 9, 10 => "A", 11 => "B", 12 => "C", 13 => "D", 14 => "E", 15 => "F");
     $remainder = $decimal;
@@ -38,6 +41,7 @@ function decimal_to_hex(int $decimal) : string {
 }
 
 function decimal_to_binary(int $decimal) : int {
+    $decimal = sanitize_int_input($decimal);
     $remainder = $decimal;
     $greatest_base_2 = 0;
     $binary_str = "";
@@ -58,6 +62,7 @@ function decimal_to_binary(int $decimal) : int {
 }
 
 function binary_to_decimal(int $binary) : int {
+    $binary = sanitize_int_input($binary);
     $digits = str_split(strrev(strval($binary)));
     $decimal = 0;
     for ($i = 0; $i < sizeof($digits); $i++) {
@@ -70,6 +75,23 @@ function binary_to_decimal(int $binary) : int {
 }
 
 function binary_to_hex(int $binary) : string {
+    $binary = sanitize_int_input($binary);
     $decimal = binary_to_decimal($binary);
     return decimal_to_hex($decimal);
+}
+
+function sanitize_int_input(int $input) : int {
+    $input = trim($input);
+    $input = stripslashes($input);
+    $input = htmlspecialchars($input);
+
+    return intval($input);
+}
+
+function sanitize_string_input(string $input) : string {
+    $input = trim($input);
+    $input = stripslashes($input);
+    $input = htmlspecialchars($input);
+
+    return strval($input);
 }