Recursive function acts weird in php - php

Question

I got stuck when I learned about recursive functions in PHP. I know recursive function are those which are being called by itself. My code is:
function addition_no($x,$y) {
if($x==0) {
return $x;
}
return addition_no($x+$y);
}
echo addition_no(1,2);
When I tried executing this code I get:
Warning: Missing argument 2 for addition_no(), called in
/web/com/13978781902261/main.php on line 6 and defined in
/web/com/13978781902261/main.php on line 2
What i need is to add two numbers via recursion.

Answer 1

I created this code in order to summarize values in an array using recursivity is:
<?php
//values to add
$add = array(5,4,4,6,7);
function addval($add,$pos) {
if($pos == 0) {
return $add[0];
}
else {
return $add[$pos] + addval($add,$pos-1);
}
}
//last position in vector
$last_position = count($add)-1;
echo addval($add, $last_position);
?>

Answer 2

You can try this
return addition_no($x,$y);
You have to check any condition for recursive function otherwise it will be infinite recursion..

Answer 3

The warning is appropriate as you call the function inside it self with a different argument structure.
Try the factorial recursive function to learn how it works:
<?php
// Initiating Recursion
echo factorial(5);
//Recursive Function Definition with 1 parameter
function factorial($number)
{
//Break condition for recursion
if($number==1)
return $number;
//Fetch and Stack Recursion
return $number*factorial($number-1);
}
So, you get the basic recursion, in simple English, as :
factorial(n) = n x factorial(n-1) = n x (n-1) x factorial(n-2)
For You particular case, you actually don't need a recursion as your arguments are not relying on the previous argument result. However, for the sake of learning, you can do something like this:
<?php
//Summation
function summation($x) {
if($x==0) {
return $x;
}
return $x+summation($x-1);
}
echo summation(5);
//Summation with 2 step
function summation($x,$y) {
if($x<1) {
return $x;
}
return $x+summation($x-$y,$y);
}
echo summation(5,2);