Palindrome in PHP

Definition of Palindrome

Before understanding, Palindrome in PHP we will first study Palindrome. Palindrome means there is no change in the original and the reverse of the string. Meaning that the palindrome of a number is the same as the original even after the reverse of the string. This can be applied to numbers also.

For Example:

Input: 12321
Reverse: 12321

Input: Civic
Reverse: Civic

To know whether a string or a number is palindrome or not we will use the built-in function in PHP.

Palindrome Logic

The logic behind getting a palindrome is as per the following:

1. Get an input number or string.
2. Get the reverse of the input number or string using the built-in function.
3. Do the comparison of both the numbers or strings – the input and the reverse number or string.
4. If the input and the reverse are found to be equal, it means that the number or string is a palindrome.

How to Check Palindrome in PHP?

To check palindrome of a number we will use the built-in function called as strrev()

About strrev() function in PHP: This function accepts both string and numbers as the input string. It performs reverse on the input string but does not change the given string. It always returns the reversed form of the given string.

Example #1

In the following program, we have an input string MADAM, on this string strrev() function is applied. The result after applying function returns the same string MADAM then a condition is checked whether the input and the reversed string are equal or not.

Code:

<?php
// example to get the palindrome of a string using built in function
//input string is MADAM
$input = "MADAM";
echo '<br> Input String '. $input;
//reverse of input string - MADAM - using strrev
$reverse = strrev($input);
echo '<br> Ouput String '. $reverse;
//condition to check if the input and the reverse of the string is equal or not
if($input == $reverse) {
echo '<br> '.$input.'  is a palindrome';
}
else {
echo '<br>'.$input.' is not a palindrome';
}
?>

Output:

Example #2

As we have seen in the above program that the input string is a palindrome. Let us apply the same strrev function on a number now to check whether the input number is a palindrome or not.

Code:

<?php
//example to get the palindrome of a number using built in function
// input string is 1234321
$input = 1234321;
echo '<br>'.'Input string '. $input;
//reverse of input string using strrev
$reverse = strrev($input);
echo '<br>'.'Reverse string '.$reverse;
//condition to check if the input and the reverse of the string is equal or not
if($input == $reverse) {
echo '<br>'.$input.' is a palindrome';
}
else {
echo '<br>'.$input.' is not a palindrome';
}
?>

Output:

Example #3

In the below program we have used the strrev() built-in function defined within a different function named Palindrome_Function. So when this function is called to reverse a string it actually performs reverse on the input string using the strrev() function. The same above program can be done in the following way.

Code:

<?php
//example to get the palindrome of a number using built in function
function Palindrome_Function($input) {
// applying strrev() function to input string
$reverse = strrev($input);
//condition to check if reverse and input strings are same or not
if($reverse == $input) {
return true;
}
else
{
return false;
}
}
$input = 1995991;
//calling the reverse function
$result = Palindrome_Function($input);
if($result == TRUE) {
echo $input.' is palindrome';
}
else
{
echo $input.' is not palindrome';
}
?>

Output:

Example #4

In the below program we will input a number which is not palindrome number and see the result.

Code:

<?php
//example to get the palindrome of a number using built in function
function Palindrome_Function($input) {
$reverse = strrev($input);
if($reverse == $input) {
return true;
}
else
{
return false;
}
}
$input = 13241;
$result = Palindrome_Function($input);
if($result == TRUE) {
echo $input.' is palindrome';
}
else
{
echo $input.' is not palindrome';
}
?>

Output:

Example #5

Following is the program wherein we have a form containing an input text box. On entering a number and submitting the form we have the result which tells us about the input number whether it is a palindrome or not.

Code:

<html>
<head>
<title>Palindrome Program</title>
</head>
<body>
<form method="post" action="program1.php">
<input type="text" name="number" value="" />
<input type="submit" name="submit" value="Submit" />
</form>
<?php
if(isset($_POST['number'])) {
$input = $_POST['number'];
$reverse = strrev($input);
if($reverse == $input) {
echo $input . 'is a palindrome';
}
else{
echo $input. 'is not a palindrome';
}
}
?>
</body>
</html>

Output:

In the below program we have the following steps to follow to get the reverse of a number without the use of strrev() function.

We will be using while loop here:

1. Get an Input number
2. Divide the number by 10 to get the remainder
3. Add the remainder to the new variable, which is multiplied by 10
4. Divide the number by 10.

Code:

<?php
//example to check if number is palindrome or not without using function only for numbers
//defining the palindrome function
function Palindrome_Function($input) {
$number = $input;
$sum = 0;
//using while loop to get the reverse of the input number
while(floor($number))
{
$remainder = $number % 10;
$sum = $sum * 10 + $remainder;
$number = $number / 10;
}
if($sum == $input) {
return true;
}
else {
return false;
}
}
//passing the input number
$input_number = 1546451;
//calling the Palindrome_Function
$result = Palindrome_Function($input_number);
//check if the input is equal to output of palindrome_function
if($result){
echo "<br>"." $input_number is a Palindrome";   //if equal show $input is palindrome number
} else {
echo "<br>"."$input_number is not a Palindrome";  //if not equal show $input is not a palindrome number
}
?>

Output:

Conclusion – Palindrome in PHP

In this article, it is explained with examples of what is a palindrome, how do we find whether a number is a palindrome or not, and how to know whether the input string is a palindrome or not. Hope this article was helpful.

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