PHP dynamic typing behavior - Step-by-Step Execution

Concept Flow - PHP dynamic typing behavior

Assign value to variable

↓

PHP stores value with type

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Use variable in expression

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PHP converts type as needed

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Perform operation with converted types

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Return or output result

PHP variables can hold any type and change type automatically depending on the value and context.

Execution Sample

PHP

<?php
$a = 5;       // integer
$a = "10";    // string
$b = $a + 2;   // string converted to int
echo $b;       // outputs 12
?>

This code shows PHP changing variable types dynamically and converting string to integer during addition.

Execution Table

Step	Variable	Value Assigned	Type	Operation	Result/Output
1	$a	5	integer	Assign 5	Value of $a is 5 (int)
2	$a	"10"	string	Assign "10"	Value of $a is "10" (string)
3	$b	$a + 2	integer	Add string "10" + int 2	PHP converts "10" to 10, $b = 12 (int)
4	echo $b	12	integer	Output $b	Outputs 12

💡 Execution ends after echo outputs 12.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$a	undefined	5 (int)	"10" (string)	10 (int)	10 (int)
$b	undefined	undefined	undefined	12 (int)	12 (int)

Key Moments - 3 Insights

Why does $a change from integer to string?

Because PHP variables are dynamically typed, assigning a string to $a changes its type immediately (see execution_table step 2).

How can PHP add a string and an integer?

PHP automatically converts the string "10" to integer 10 when used in addition (see execution_table step 3).

What type is $b after addition?

$b is an integer because PHP converts operands to numbers before adding (see execution_table step 3).

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the type of $a?

A integer

B string

C float

D boolean

💡 Hint

Check the 'Type' column in execution_table row for step 2.

At which step does PHP convert a string to an integer for addition?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Operation' and 'Result/Output' columns in execution_table.

If $a was assigned "5 apples" instead of "10", what would happen at step 3?

A $b would be 7

B $b would be 0

C $b would be 5

D PHP would throw an error

💡 Hint

PHP converts strings starting with numbers to those numbers in arithmetic (see variable_tracker and PHP dynamic typing rules).

Concept Snapshot

PHP variables have no fixed type.
Assigning a new value changes the variable's type.
In expressions, PHP converts types automatically.
Strings with numbers convert to numbers in math.
This is called dynamic typing.

Full Transcript

This example shows PHP's dynamic typing behavior. First, $a is assigned the integer 5. Then $a is assigned the string "10", changing its type. When $b is assigned $a + 2, PHP converts the string "10" to integer 10 to perform addition. Finally, echo outputs 12. PHP variables can hold any type and change type automatically depending on the assigned value and usage context.