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

Concept Flow - While loop execution model

Initialize variable

↓

Check condition

|Yes↓

Execute loop body

↓

Update variable

Back to Check condition↓

Exit loop

↩Back to Check condition

The while loop starts by checking a condition. If true, it runs the loop body, updates variables, then checks the condition again. It stops when the condition is false.

Execution Sample

PHP

<?php
$i = 1;
while ($i <= 3) {
    echo $i . " ";
    $i++;
}
?>

This code prints numbers 1 to 3 using a while loop that runs while $i is less than or equal to 3.

Execution Table

Step	Variable $i	Condition ($i <= 3)	Action	Output
1	1	True	Print 1, increment $i to 2	1
2	2	True	Print 2, increment $i to 3	2
3	3	True	Print 3, increment $i to 4	3
4	4	False	Exit loop

💡 $i is 4, condition 4 <= 3 is False, loop stops

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$i	1	2	3	4	4

Key Moments - 2 Insights

Why does the loop stop when $i is 4?

Because the condition $i <= 3 becomes false at step 4, so the loop exits as shown in the execution_table row 4.

When is the variable $i incremented in the loop?

The variable $i is incremented after printing, inside the loop body, as seen in the 'Action' column of the execution_table rows 1 to 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $i at Step 3?

A 2

B 4

C 3

D 1

💡 Hint

Check the 'Variable $i' column at Step 3 in the execution_table.

At which step does the condition become false and the loop stops?

A Step 4

B Step 3

C Step 2

D Step 1

💡 Hint

Look at the 'Condition' column in the execution_table to find when it is false.

If we start $i at 0 instead of 1, how many times will the loop run?

A 3 times

B 4 times

C 2 times

D 1 time

💡 Hint

Refer to variable_tracker and consider the condition $i <= 3 starting from 0.

Concept Snapshot

while (condition) {
  // code to run
  // update variables
}

- Checks condition before each loop
- Runs loop body only if condition is true
- Stops when condition is false
- Update variables inside loop to avoid infinite loop

Full Transcript

This example shows how a while loop works in PHP. We start with a variable $i set to 1. The loop checks if $i is less than or equal to 3. If yes, it prints $i and then increases $i by 1. This repeats until $i becomes 4, when the condition fails and the loop stops. The execution table tracks each step, showing variable values, condition results, actions, and output. The variable tracker shows how $i changes after each step. Key moments explain why the loop stops and when $i is incremented. The quiz asks about variable values and loop behavior based on the tables. The snapshot summarizes the while loop syntax and rules.