For loop execution model in PHP - Step-by-Step Execution

Concept Flow - For loop execution model

Initialize i=0

↓

Check: i < 3?

No→EXIT

Yes↓

Execute body: print i

↓

Update: i = i+1

↩Back to Check

The loop starts by setting i to 0, then checks if i is less than 3. If yes, it runs the loop body, then increases i by 1 and repeats. If no, it stops.

Execution Sample

PHP

<?php
for ($i = 0; $i < 3; $i++) {
    echo $i . "\n";
}
?>

This PHP code prints numbers 0, 1, and 2 each on a new line using a for loop.

Execution Table

Iteration	i before condition	Condition (i < 3)	Body executed	Output	i after update
1	0	True	Yes	0	1
2	1	True	Yes	1	2
3	2	True	Yes	2	3
4	3	False	No

💡 i reaches 3, condition 3 < 3 is False, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	0	1	2	3	3

Key Moments - 3 Insights

Why does the loop stop when i equals 3?

Because the condition i < 3 becomes False at iteration 4 (see execution_table row 4), so the loop does not run the body again.

When is the variable i updated in the loop?

i is updated after the loop body executes each time (see execution_table column 'i after update'), before the next condition check.

What is printed during each iteration?

The current value of i before it is incremented is printed (see execution_table 'Output' column for iterations 1 to 3).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i before the condition check in iteration 3?

A 3

B 2

C 1

D 0

💡 Hint

Check the 'i before condition' column in row 3 of the execution_table.

At which iteration does the loop condition become false?

A Iteration 4

B Iteration 1

C Iteration 3

D Iteration 2

💡 Hint

Look at the 'Condition (i < 3)' column and find where it is False.

If the loop condition changed to i < 2, how many times would the loop body execute?

A 3 times

B 1 time

C 2 times

D 0 times

💡 Hint

Refer to the variable_tracker and execution_table to see how condition affects iterations.

Concept Snapshot

PHP for loop syntax:
for (initialization; condition; update) {
  // code to run
}

Loop runs while condition is true.
Initialization runs once at start.
Update runs after each loop body execution.
Loop stops when condition is false.

Full Transcript

This visual execution model shows how a PHP for loop works step-by-step. The loop starts by setting i to 0. Then it checks if i is less than 3. If yes, it runs the loop body which prints i, then increases i by 1. This repeats until i reaches 3, when the condition becomes false and the loop stops. The execution table tracks each iteration's variable values, condition results, and outputs. The variable tracker shows how i changes from 0 to 3. Key moments clarify why the loop stops at 3 and when i updates. The quiz tests understanding of variable values and loop behavior. This helps beginners see exactly how the for loop runs in PHP.