If statement execution flow in PHP - Step-by-Step Execution

Concept Flow - If statement execution flow

Start

↓

Evaluate condition

↓

Execute if-block

↓

Continue

↓

Skip if-block

↓

Continue

The program checks the condition. If true, it runs the code inside the if-block. If false, it skips it and continues.

Execution Sample

PHP

<?php
$age = 20;
if ($age >= 18) {
    echo "Adult";
}
?>

Checks if age is 18 or more, then prints 'Adult' if true.

Execution Table

Step	Condition ($age >= 18)	Result	Branch Taken	Output
1	20 >= 18	True	Execute if-block	Adult
2	End of if statement	-	Continue	-

💡 Condition true, executed if-block and printed 'Adult', then continued.

Variable Tracker

Variable	Start	After Step 1	Final
$age	20	20	20

Key Moments - 2 Insights

Why does the code inside the if-block run only when the condition is true?

Because the if statement checks the condition first (see execution_table step 1). If true, it runs the block; if false, it skips it.

What happens if the condition is false?

The program skips the if-block and continues (not shown here, but see concept_flow and execution_table branch 'No').

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 1?

A Error

B Adult

C No output

D 20

💡 Hint

Check the 'Output' column in execution_table row for step 1.

At which step does the program decide to skip the if-block?

A Step 1

B Step 2

C Never in this example

D Before step 1

💡 Hint

Look at the 'Branch Taken' column in execution_table; the if-block is executed at step 1.

If $age was 16, how would the execution_table change at step 1?

A Condition would be false, branch would skip if-block

B Condition would be true, branch would execute if-block

C Output would be 'Adult'

D Program would crash

💡 Hint

Refer to the condition evaluation in execution_table and concept_flow for false branch.

Concept Snapshot

if (condition) {
  // code runs if condition is true
}

Checks condition once.
Runs block only if true.
Skips block if false.
Then continues program.

Full Transcript

This visual shows how an if statement works in PHP. The program starts and checks the condition inside the if statement. If the condition is true, it runs the code inside the if-block. If false, it skips that code and continues. In the example, the variable $age is 20. The condition $age >= 18 is true, so the program prints 'Adult'. The variable $age stays the same throughout. Beginners often wonder why the code runs only when the condition is true; this is because the if statement controls that flow. If the condition was false, the code inside would be skipped. The quiz questions help check understanding of these steps.

Practice

1. What does an if statement do in PHP?

easy

A. It defines a function.

B. It repeats code multiple times.

C. It runs code only if a condition is true.

D. It stops the program immediately.

Solution

1. Step 1: Understand the purpose of an if statement

   An if statement checks a condition and runs code only if that condition is true.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define reusable code, and stopping the program is done by exit or die.

3. Final Answer:

   It runs code only if a condition is true. -> Option C

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If checks condition; runs code only when true [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if defines functions
• Believing if stops the program

2. Which of the following is the correct syntax for an if statement in PHP?

easy

A. if condition { echo 'Yes'; }

B. if (condition) { echo 'Yes'; }

C. if condition: echo 'Yes'; endif;

D. if [condition] { echo 'Yes'; }

Solution

1. Step 1: Recall PHP if statement syntax

   In PHP, the condition must be inside parentheses and the code block inside curly braces.

2. Step 2: Check each option

   if (condition) { echo 'Yes'; } matches the correct syntax: if (condition) { ... }. if condition { echo 'Yes'; } misses parentheses, C uses alternate syntax but missing parentheses, D uses square brackets which is invalid.

3. Final Answer:

   if (condition) { echo 'Yes'; } -> Option B

4. Quick Check:

   Parentheses around condition = correct syntax [OK]

Hint: Always use parentheses around condition in if [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using square brackets instead of parentheses
• Confusing alternate syntax without proper format

3. What will be the output of this PHP code?

$x = 10;
if ($x > 10) {
  echo 'Greater';
} elseif ($x == 10) {
  echo 'Equal';
} else {
  echo 'Less';
}

medium

A. Equal

B. No output

C. Less

D. Greater

Solution

1. Step 1: Evaluate the condition $x > 10

   $x is 10, so $x > 10 is false. The first if block is skipped.

2. Step 2: Check the elseif condition $x == 10

   This condition is true, so it prints 'Equal' and skips the else block.

3. Final Answer:

   Equal -> Option A

4. Quick Check:

   10 == 10 prints Equal [OK]

Hint: Check conditions top to bottom; first true runs [OK]

Common Mistakes:

• Assuming > includes equal
• Ignoring elseif and jumping to else
• Thinking multiple blocks run

4. Find the error in this PHP code:

if $a > 5 {
  echo 'Big';
} else {
  echo 'Small';
}

medium

A. Wrong keyword else

B. Missing semicolon after echo

C. Curly braces not allowed

D. Missing parentheses around condition

Solution

1. Step 1: Check if statement syntax

   In PHP, the condition must be inside parentheses. Here, if $a > 5 is missing parentheses.

2. Step 2: Verify other parts

   Semicolons after echo statements are optional if echo is used as a statement, else keyword is correct, and curly braces are allowed.

3. Final Answer:

   Missing parentheses around condition -> Option D

4. Quick Check:

   Condition must be in parentheses [OK]

Hint: Always put condition inside parentheses in if [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Thinking else keyword is wrong
• Believing semicolon is mandatory after echo

5. Given this PHP code, what will be the output?

$score = 75;
if ($score >= 90) {
  echo 'A';
} elseif ($score >= 80) {
  echo 'B';
} elseif ($score >= 70) {
  echo 'C';
} else {
  echo 'F';
}

hard

A. C

B. A

C. B

D. F

Solution

1. Step 1: Check first condition $score >= 90

   75 is less than 90, so this is false. Skip to next.

2. Step 2: Check second condition $score >= 80

   75 is less than 80, so false again. Skip to next.

3. Step 3: Check third condition $score >= 70

   75 is greater than or equal to 70, so true. It prints 'C' and skips else.

4. Final Answer:

   C -> Option A

5. Quick Check:

   75 >= 70 prints C [OK]

Hint: Check conditions top-down; first true runs [OK]

Common Mistakes:

• Choosing wrong grade for score
• Ignoring elseif order
• Assuming else runs always