Project: Calculator

Overview of the 5-lesson calculator project: you will operate on two numbers and an operator.

Project: Calculator

In this 5-lesson project you'll build a calculator. Each lesson adds one piece, and by the final lesson you'll have a complete app.

You'll use what you learned before:

variables with the $ sign
output with echo
string and int types
variable concatenation

You'll also learn the if/elseif structure and arithmetic operators in this project. Ready? Let's start.

The calculator flow

The calculator works in four steps:

Input: two numbers are taken.
Operation: an operator is chosen (+, -, *, /).
Compute: the result is found based on the operator.
Output: the result is printed.

In the first lesson we'll just take one number and print it. The next lessons add the operator, the second number and the compute step. Each lesson grows the calculator by one step.

Exercise Declare the first number and print it

In this lesson you'll write the first piece of the calculator. Assign 25 to the $first variable and print it with echo.

Show example solution

Declare the variable with $ and print it with echo.
Example solution:
<?php
// The first number entered by the user
$first = 25;
echo $first;

Test yourself

What does a calculator need first to work?
- A file
- Two numbers and an operation
- A database
- A class
Show answer

Two numbers and an operation — A calculator takes two numbers and performs an operation between them.
Match each calculator step to its description

Input

Two numbers are taken
Operation

Operator is chosen
Compute

Result is found
Output

Result is printed

Assign 25 to the first number variable

<?php
$first = ____;
echo $first;
?>

Show answer

<?php
$first = 25;
echo $first;
?>

Next lesson: Number input and operator selection

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