Nested conditional execution in PHP - Step-by-Step Execution

Concept Flow - Nested conditional execution

Start

↓

Check Condition 1

|Yes↓

Check Condition 2

|Yes↓

Execute Inner Block

↓

End Inner Block

↓

End Outer Block

↓

End

No↓

Skip Inner Block

↓

End

First, the outer condition is checked. If true, the inner condition is checked next. If both are true, the inner block runs. Otherwise, it skips.

Execution Sample

PHP

<?php
$age = 20;
if ($age >= 18) {
  if ($age < 21) {
    echo "You are an adult but not allowed to drink.";
  }
}
?>

This code checks if age is 18 or more, then checks if it is less than 21, and prints a message if both are true.

Execution Table

Step	Variable $age	Condition 1 ($age >= 18)	Condition 2 ($age < 21)	Action	Output
1	20	True	Not checked yet	Check outer condition
2	20	True	True	Check inner condition
3	20	True	True	Execute inner block	You are an adult but not allowed to drink.
4	20	True	True	End

💡 Both conditions true, inner block executed, then program ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$age	20	20	20	20	20

Key Moments - 2 Insights

Why is the inner condition only checked if the outer condition is true?

Because the inner if is inside the outer if block, so it runs only when the outer condition is true, as shown in steps 1 and 2 of the execution table.

What happens if the outer condition is false?

The inner condition is never checked and the inner block is skipped, so no output is produced. This is implied by the flow and the exit note.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of Condition 1 at step 1?

A Not checked

B True

C False

D Unknown

💡 Hint

Check the 'Condition 1' column in row for step 1 in the execution table.

At which step is the inner condition ($age < 21) evaluated?

A Step 3

B Step 1

C Step 2

D Never

💡 Hint

Look at the 'Condition 2' column in the execution table to see when it changes from 'Not checked yet' to a value.

If $age was 17, what would happen in the execution table?

A Condition 1 would be false, inner condition not checked, no output

B Both conditions true, inner block executed

C Only inner condition checked

D Output printed regardless of conditions

💡 Hint

Refer to the key moment about what happens if the outer condition is false.

Concept Snapshot

Nested conditional execution in PHP:
if (condition1) {
  if (condition2) {
    // code runs only if both true
  }
}
Inner condition runs only if outer is true.
Useful for step-by-step checks.

Full Transcript

This example shows nested conditional execution in PHP. First, the program checks if the variable $age is 18 or more. If yes, it then checks if $age is less than 21. Only if both conditions are true, it prints a message. The execution table shows each step: checking the outer condition, then the inner condition, then running the inner block. The variable $age stays the same throughout. Beginners often wonder why the inner condition is not checked if the outer is false; this is because the inner if is inside the outer if block. If $age was less than 18, the inner condition would never run and no output would appear. This step-by-step trace helps understand how nested if statements work in PHP.