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PHP Build a Simple PHP Application Integrating with PayPal Including the Products Array

Steven Griffiths
Steven Griffiths
3,165 Points
Posted by Steven Griffiths
Steven Griffiths
3,165 Points

Why do we use concatenation to add the $product_id to the end of the web address

Hi.

Can't quite get my head around this.

Why do we have to concatenate here? can't we just write something like this:

echo '<a href="shirt.php?id=$product_id">';

Thanks in advance

2 Answers

Muhammad Mohsen
Muhammad Mohsen
Courses Plus Student 10,843 Points

Hi Steven,

Because you have single quotation surrounding your string you can't echo it like that 

<?php echo '<a href="shirt.php?id=$product_id">'; ?>

the result will be string

<a href="shirt.php?id=$product_id">

In other words, it will consider $product_id as string NOT a variable.

you may also echo it like that:

<?php echo "<a href='shirt.php?id=$product_id'>"; ?>

Simply replace 'single quotations' with "double quotations", Now you can embed variables inside it and it will work just fine.

Steven Griffiths
Steven Griffiths
3,165 Points
Steven Griffiths
Steven Griffiths
3,165 Points

aaah! nice. thanks Muhammad.

Andrew Shook
Andrew Shook
31,709 Points
Andrew Shook
Andrew Shook
31,709 Points

Just to add to Muhammad's earlier comment, if you are using the "double quotes" you can also do it like this so the variable stands out a little:

<?php echo "<a href='shirt.php?id={$product_id}'>"; ?>

On almost all the IDE I've used, if you wrap the variable in curly braces it will change the color so that spotting the variable in the string is easier.

Jeff Busch
Jeff Busch
19,287 Points
Jeff Busch
Jeff Busch
19,287 Points

Hi Steven,

If you try it your way you will see that the string "$product_id" is echoed instead of the value of $product_id. Run this code and hover your mouse pointer over the links and look at where the link points.

Jeff

<?php

$product_id = 13;

echo '<a href="shirt.php?id=' . $product_id . '">Link 1</a><br>';

echo '<a href="shirt.php?id=$product_id">Link 2</a>';

?>
Jeff Busch
Jeff Busch
19,287 Points

Another way to write that line of code is:

<?php
printf('<a href="shirt.php?id=%d">Link 2</a><br>', $product_id);
?>

Personally, I find the printf() method less confusing.

Steven Griffiths
Steven Griffiths
3,165 Points
Steven Griffiths
Steven Griffiths
3,165 Points

Great. That helped a lot.

Many thanks Jeff.