How Can I Build a PHP Calculator Using the Shunting Yard Algorithm?

How to Create a Calculator Using PHP

Problem:

You want to develop a PHP calculator that evaluates simple algebraic expressions inputted by users in standard notation, displaying the evaluation process. The challenge lies in efficiently calculating the expression's value.

Answer:

Consider utilizing the Shunting Yard Algorithm for its simplicity and efficiency in evaluating algebraic expressions.

Shunting Yard Algorithm Implementation

Expression Definitions:

Create classes to represent different elements of the expression, such as parentheses, numbers, operators, and so on:

class Parenthesis extends TerminalExpression { ... }
class Number extends TerminalExpression { ... }
class Addition extends Operator { ... }
class Subtraction extends Operator { ... }
class Multiplication extends Operator { ... }
class Division extends Operator { ... }
class Power extends Operator { ... }

Stack Implementation:

class Stack {

    protected $data = array();

    // ... Methods for pushing, popping, and peeking from the stack ...
        
}

Executor Class:

The executor class parses the expression using the Shunting Yard algorithm and evaluates it:

class Math {

    // ... Fields and methods for parsing, running, and evaluating the expression ...
        
}

Example:

Here's an example of how to use the calculator:

$math = new Math();

$answer = $math->evaluate('(2 + 3) * 4');
var_dump($answer);
// int(20)

$answer = $math->evaluate('1 + 2 * ((3 + 4) * 5 + 6)');
var_dump($answer);
// int(83)

This example covers grouping and operator precedence. However, you can customize the implementation to suit your specific requirements.

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