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Chapter 10 Question About Variables Inside Of Functions

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<meta http-equiv="content-type" content="text/html; charset=utf-8"/>
<title>Cost Calculator</title>
<?php  // Script 10.4 - calculator.php
/* this script displays and handles an HTML form.
It uses a function to calculate a total from a quantity and price. */
//this function returns the calculations
function calculate_total ($quantity, $price) {
$total = $quantity * $price; //calculation
$total = number_format ($total, 2); //formatting

return $total;  //return the value.

} //end of calculate_total() function
//check for form submisstion

//form validation
if (is_numeric($_POST['quantity']) && is_numeric($_POST['price'])) {

 //call the function and print the results
 $total = calculate_total($_POST['quantity'], $_POST['price']);
 print "<p>Your total comes to $<span style=\"font-weight: bold;\">$total.</span></p>";

} else {

 print '<p style="color: red;">Please make sure to enter only numbers into the calculator.</p>';

} // end of form validation

}  // end of if checking form has been submitted.

<form action="calculator.php" method="POST">
<p>Quantity: <input type="text" name="quantity" size="3" /></p>
<p>Price: <input type="text" name="price" size="3" /></p>
<p><input type="submit" name="submit" value="Calculate!" /></p>


Are variables located inside of functions separate from variables located outside of functions?


For example in the above code, the calculate_total() function returns the variable $total. But later on in the script, I assign $total to this:

 $total = calculate_total($_POST['quantity'], $_POST['price']);   


By doing that am I overwriting the $total variable? My guess is that the answer is no, because I tried changing the $total variable to something different, for example to $sum, like this:

//call the function and print the results
 $sum = calculate_total($_POST['quantity'], $_POST['price']);
 print "<p>Your total comes to $<span style=\"font-weight: bold;\">$sum.</span></p>"; 


and the function still worked properly. I was just looking for a little clarification on this.





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You might also want to check out the variable scope section a little further on in chapter 10.


Thanks. Yeah I stopped for the night just before the 'Variable Scope' section :). After just reading it, it makes a lot more sense. What exactly answered my question was this:


page 279: Function variables - the arguments of a function as well as any ariables defined within the function - exist only within that function and aren't accessible outside of it.


also page 280: Because of variable scope, a local variable within a function is a different entity than a variable outside of the function, even if the two variables use the exact same name.



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  • 2 months later...

If the function only uses echo or print, then the only thing the function can do is send that value to the browser. If a function returns a value, then it can be used in any kind of way, including echo or print at a later point. For example, if a function calculated a shipping cost, if the function only printed that calculated value, then it couldn't be stored in a database, used in a payment process, or sent as part of an email receipt.

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  • 2 months later...

That's correct.

function make_full_name($first, $last) {
return $name=$first . ' ' . $last;


In your calling script, call the function with the 2 arguments and store the return value in a variable.

$fullname  = make_full_name($fname, $lname);


You can then use $fullname in the calling script to do whatever - echo to the browser, send as part of an email, insert to a database.

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