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

Concept Flow - If-else execution flow

Start

↓

Evaluate condition

↓

Execute if-block

↓

End

↓

Execute else-block

↓

End

The program checks a condition. If true, it runs the if-block. Otherwise, it runs the else-block. Then it ends.

Execution Sample

PHP

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

This code checks if age is 18 or more, prints 'Adult' if true, else prints 'Minor'.

Execution Table

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

💡 Condition is true, so if-block runs and program ends after printing 'Adult'.

Variable Tracker

Variable	Start	After Step 1	Final
$age	18	18	18

Key Moments - 2 Insights

Why does the program print 'Adult' and not 'Minor'?

Because at Step 1 in the execution_table, the condition ($age >= 18) is true, so the if-block runs and prints 'Adult'. The else-block is skipped.

What happens if the condition is false?

If the condition was false, the else-block would run instead, printing 'Minor'. This is shown by the 'Branch Taken' column in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output at Step 1?

A Minor

B 18

C Adult

D No output

💡 Hint

Check the 'Output' column at Step 1 in the execution_table.

At which step does the program decide which block to run?

A Step 2

B Step 1

C Before Step 1

D After Step 2

💡 Hint

Look at the 'Condition' and 'Branch Taken' columns in the execution_table.

If $age was 16, how would the 'Branch Taken' change in the execution_table?

A It would change to 'else-block'

B It would still be 'if-block'

C No branch would be taken

D Both blocks would run

💡 Hint

Refer to the 'Condition' and 'Branch Taken' logic in the execution_table.

Concept Snapshot

if (condition) {
  // code if true
} else {
  // code if false
}

Checks condition once.
Runs if-block if true.
Runs else-block if false.

Full Transcript

This PHP code uses an if-else statement to check if the variable $age is 18 or more. If true, it prints 'Adult'. Otherwise, it prints 'Minor'. The execution flow starts by evaluating the condition $age >= 18. Since $age is 18, the condition is true, so the if-block runs and outputs 'Adult'. The else-block is skipped. Variables remain unchanged during this process. This flow helps decide between two paths based on a condition.

Practice

1. What does an if-else statement do in PHP?

easy

A. It repeats code multiple times.

B. It chooses one block of code to run based on a condition.

C. It runs all blocks of code regardless of conditions.

D. It defines a function.

Solution

1. Step 1: Understand the purpose of if-else

   An if-else statement checks a condition and runs code based on whether the condition is true or false.

2. Step 2: Compare options with definition

   Only "It chooses one block of code to run based on a condition." correctly describes this behavior; others describe loops or functions.

3. Final Answer:

   It chooses one block of code to run based on a condition. -> Option B

4. Quick Check:

   If-else = choose one path [OK]

Hint: If-else picks one path based on true or false [OK]

Common Mistakes:

• Thinking if-else runs all code blocks
• Confusing if-else with loops
• Believing if-else defines functions

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

easy

A. if ($x > 10) { echo 'Yes' } else { echo 'No' }

B. if $x > 10 then echo 'Yes' else echo 'No'

C. if ($x > 10) echo 'Yes' else echo 'No'

D. if ($x > 10) { echo 'Yes'; } else { echo 'No'; }

Solution

1. Step 1: Check PHP if-else syntax rules

   PHP requires parentheses around the condition and braces around the code blocks.

2. Step 2: Identify correct syntax

   if ($x > 10) { echo 'Yes'; } else { echo 'No'; } uses parentheses and braces correctly. if $x > 10 then echo 'Yes' else echo 'No' uses invalid keywords. if ($x > 10) echo 'Yes' else echo 'No' misses braces which is allowed but needs semicolons. if ($x > 10) { echo 'Yes' } else { echo 'No' } misses semicolons inside braces.

3. Final Answer:

   if ($x > 10) { echo 'Yes'; } else { echo 'No'; } -> Option D

4. Quick Check:

   Correct syntax = if ($x > 10) { echo 'Yes'; } else { echo 'No'; } [OK]

Hint: Use parentheses and braces with semicolons in PHP if-else [OK]

Common Mistakes:

• Omitting parentheses around condition
• Missing semicolons after statements
• Using invalid keywords like 'then'

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

$score = 75;
if ($score >= 60) {
    echo "Pass";
} else {
    echo "Fail";
}

medium

A. Pass

B. Fail

C. 60

D. No output

Solution

1. Step 1: Evaluate the condition $score >= 60

   The variable $score is 75, which is greater than or equal to 60, so the condition is true.

2. Step 2: Determine which block runs

   Since the condition is true, the code inside the if block runs, printing "Pass".

3. Final Answer:

   Pass -> Option A

4. Quick Check:

   75 >= 60 is true, so output = Pass [OK]

Hint: Check if condition is true to pick if or else output [OK]

Common Mistakes:

• Confusing true and false branches
• Ignoring comparison operators
• Expecting numeric output instead of string

4. Find the error in this PHP code snippet:

if ($age > 18)
    echo "Adult";
else
    echo "Minor"

medium

A. Missing parentheses around condition

B. Missing braces around if and else blocks

C. Missing semicolon after echo "Minor"

D. Incorrect comparison operator

Solution

1. Step 1: Check syntax for echo statements

   Each echo statement must end with a semicolon in PHP.

2. Step 2: Identify missing semicolon

   The echo "Minor" line is missing a semicolon at the end, causing a syntax error.

3. Final Answer:

   Missing semicolon after echo "Minor" -> Option C

4. Quick Check:

   Every statement needs semicolon [OK]

Hint: Always end echo statements with semicolon [OK]

Common Mistakes:

• Forgetting semicolon after last statement
• Thinking braces are always required
• Misreading comparison operators

5. You want to write a PHP program that prints "Good morning" if the hour is less than 12, "Good afternoon" if the hour is between 12 and 17 (inclusive), and "Good evening" otherwise. Which code correctly implements this using if-else statements?

hard

A. if ($hour < 12) {
echo "Good morning";
} else if ($hour <= 17) {
echo "Good afternoon";
} else {
echo "Good evening";
}

B. if ($hour < 12) {
echo "Good morning";
} else if ($hour > 12 && $hour < 17) {
echo "Good afternoon";
} else {
echo "Good evening";
}

C. if ($hour <= 12) {
echo "Good morning";
} else if ($hour >= 12 && $hour <= 17) {
echo "Good afternoon";
} else {
echo "Good evening";
}

D. if ($hour < 12) {
echo "Good morning";
} else if ($hour >= 12 && $hour < 17) {
echo "Good afternoon";
} else {
echo "Good evening";
}

Solution

1. Step 1: Analyze the conditions for each greeting

   "Good morning" if hour < 12, "Good afternoon" if hour between 12 and 17 inclusive, else "Good evening".

2. Step 2: Check each option's condition ranges

   if ($hour < 12) { echo "Good morning"; } else if ($hour <= 17) { echo "Good afternoon"; } else { echo "Good evening"; } correctly uses $hour < 12, then $hour <= 17 for afternoon, covering 12 to 17 inclusive. Others either exclude 12 or 17 or overlap incorrectly.

3. Final Answer:

   if ($hour < 12) { echo "Good morning"; } else if ($hour <= 17) { echo "Good afternoon"; } else { echo "Good evening"; } -> Option A

4. Quick Check:

   Correct ranges cover all hours without gaps [OK]

Hint: Check boundary conditions carefully in if-else chains [OK]

Common Mistakes:

• Using wrong comparison operators for boundaries
• Overlapping or missing hour ranges
• Confusing inclusive and exclusive conditions