PHP Total of Var & Constant

[JSEB]

I am fairly new to PHP, I am trying to get the total for a variable and a constant.
My variable is a random integer, and I need the total of $shirts bought, to match the price point I have set as my constant 'SHIRT_PRICE'
I hope I explained this well, the code I have currently:

<?php
    define ('SHIRT_PRICE', '17.99');
    $shirts = rand(1, 10);
    echo $shirts_total = ($shirts += 'SHIRT_PRICE');

The error I am getting: Fatal error: Uncaught TypeError: Unsupported operand types: int + string in C:\xampp\htdocs\clothing_sales.php:32 Stack trace: #0 {main} thrown in C:\xampp\htdocs\clothing_sales.php on line 32

 

[Damien]

$shirts_total = ($shirts += 'SHIRT_PRICE')

Should be:

$shirts_total = ($shirts += SHIRT_PRICE)

By adding the single quotes you're not returning the value from the constant, you're creating a string with the same name.

 

[JSEB]

$shirts_total = ($shirts += 'SHIRT_PRICE')

Should be:

$shirts_total = ($shirts += SHIRT_PRICE)

By adding the single quotes you're not returning the value from the constant, you're creating a string with the same name.

wow thank you