Operator precedence and evaluation in PHP - Mini Project: Build & Apply

Operator precedence and evaluation

📖 Scenario: Imagine you are calculating the total cost of items in a shopping cart with discounts and taxes applied. Understanding how PHP evaluates expressions with different operators helps you get the correct total.

🎯 Goal: You will write PHP code that uses variables and arithmetic operators. You will learn how operator precedence affects the calculation result.

📋 What You'll Learn

Create variables with exact values for item price, quantity, discount rate, and tax rate.

Create a variable for the discount threshold.

Calculate the total price applying discount only if quantity is above the threshold, then add tax.

Print the final total price.

💡 Why This Matters

🌍 Real World

Calculating prices with discounts and taxes is common in online shopping carts and billing systems.

💼 Career

Understanding operator precedence helps developers avoid bugs in financial calculations and write clear, correct code.

1

DATA SETUP: Create variables for item price, quantity, discount rate, and tax rate

Create four variables with these exact names and values: $itemPrice = 50;, $quantity = 3;, $discountRate = 0.1;, and $taxRate = 0.07;

PHP

<?php

// Create variables for item price, quantity, discount rate, and tax rate
// Your code here

Need a hint?

Use the $ sign for variable names and assign the exact values given.

2

CONFIGURATION: Create a discount threshold variable

Create a variable called $discountThreshold and set it to 2

PHP

<?php
$itemPrice = 50;
$quantity = 3;
$discountRate = 0.1;
$taxRate = 0.07;
// Create a discount threshold variable
// Your code here

Need a hint?

Remember to use $discountThreshold as the variable name and assign the value 2.

3

CORE LOGIC: Calculate total price with discount and tax using operator precedence

Create a variable called $totalPrice that calculates the total price as follows: multiply $itemPrice by $quantity, then subtract the discount only if $quantity is greater than $discountThreshold (discount is $itemPrice * $quantity * $discountRate), then add tax on the discounted amount (tax is $totalPrice * $taxRate). Use parentheses to ensure correct operator precedence.

PHP

<?php
$itemPrice = 50;
$quantity = 3;
$discountRate = 0.1;
$taxRate = 0.07;
$discountThreshold = 2;
// Calculate total price with discount and tax
// Your code here

Need a hint?

Use the ternary operator condition ? true_value : false_value to apply discount only if quantity is above threshold. Use parentheses to control the order of operations.

4

OUTPUT: Print the final total price

Write a print statement to display the value of $totalPrice.

PHP

 $discountThreshold) ? $itemPrice * $quantity * $discountRate : 0)) * (1 + $taxRate);
// Print the total price
// Your code here

Need a hint?

Use print($totalPrice); to show the final result.