How to call function of one php file from another php file and pass parameters to it?

I want to call a function in one PHP file from a second PHP file and also pass two parameters to that function. How can I do this?

I am very new to PHP. So please tell me, should I include the first PHP file into the second?

Please show me an example. You can provide some links if you want.

Yes require the first file into the second. That's all.

See an example below,

File1.php :

<?php
function first($int, $string){ //function parameters, two variables.
    return $string;  //returns the second argument passed into the function
}

Now Using require (http://php.net/require) to require the File1.php to make its content available for use in the second file:

File2.php :

<?php
require __DIR__ . '/File1.php';
echo first(1, "omg lol"); //returns omg lol;

file1.php

<?php

	function func1($param1, $param2)
	{
		echo $param1 . ', ' . $param2;
	}

file2.php

<?php

	require_once('file1.php');

	func1('Hello', 'world');

See manual

files directory:

Project->

-functions.php

-main.php

functions.php

function sum(a,b){
 return a+b;
}
function product(a,b){
return a*b;
}

main.php

require_once "functions.php";
echo "sum of two numbers ". sum(4,2);
echo "<br>"; //  create break line
echo "product of two numbers ".product(2,3);

The Output Is :

sum of two numbers 6 product of two numbers 6

Note: don't write public before function. Public, private, these modifiers can only use when you create class.

you can write the function in a separate file (say common-functions.php) and include it wherever needed.

function getEmployeeFullName($employeeId) {
// Write code to return full name based on $employeeId
}

You can include common-functions.php in another file as below.

include('common-functions.php');
echo 'Name of first employee is ' . getEmployeeFullName(1);

You can include any number of files to another file. But including comes with a little performance cost. Therefore include only the files which are really required.