Comments in PHP - Step-by-Step Execution

Concept Flow - Comments in PHP

Start PHP code

↓

Read line

↓

Is line a comment?

Yes→Ignore line, no output

No↓

Execute line

↓

More lines?

Yes→Read next line

No↓

End PHP code

PHP reads each line, ignores comment lines, and executes only the code lines.

Execution Sample

PHP

<?php
// This is a single-line comment
# Another single-line comment
/* This is a
   multi-line comment */
echo "Hello"; // Prints Hello
?>

This code shows different PHP comment styles and prints 'Hello'.

Execution Table

Step	Line Content	Is Comment?	Action	Output
1	<?php	No	Start PHP code
2	// This is a single-line comment	Yes	Ignore line
3	# Another single-line comment	Yes	Ignore line
4	/* This is a	Yes	Ignore line
5	multi-line comment */	Yes	Ignore line
6	echo "Hello"; // Prints Hello	No	Execute echo statement	Hello
7	?>	No	End PHP code

💡 Reached end of PHP code, all comments ignored, only echo outputs 'Hello'

Variable Tracker

Variable	Start	After Step 6	Final
Output	""	"Hello"	"Hello"

Key Moments - 3 Insights

Why does the line with // not produce any output?

Because lines starting with // are comments, PHP ignores them as shown in steps 2 and 6 in the execution_table.

Does the multi-line comment affect the output?

No, the multi-line comment between steps 4 and 5 is ignored by PHP, so it does not affect the output.

What happens to the code after the comment on the echo line?

PHP executes the code before the comment (echo "Hello"), and ignores the comment after //, so it prints 'Hello' only.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after step 6?

A "// This is a single-line comment"

B "Hello"

C ""

D "# Another single-line comment"

💡 Hint

Check the Output column at step 6 in the execution_table.

At which step does PHP stop ignoring comment lines and produce output?

A Step 6

B Step 4

C Step 2

D Step 7

💡 Hint

Look at the Action and Output columns in the execution_table.

If the multi-line comment was removed, how would the output change?

A Output would be empty

B Output would include the comment text

C Output would be "Hello" as before

D Code would cause an error

💡 Hint

Refer to the key_moments about multi-line comments and the execution_table rows 4 and 5.

Concept Snapshot

PHP comments start with // or # for single-line, and /* */ for multi-line.
Comments are ignored by PHP and do not affect output.
Code after comments runs normally.
Use comments to explain code without changing behavior.

Full Transcript

This visual trace shows how PHP reads code line by line. Lines starting with //, #, or enclosed in /* */ are comments and ignored. Only code lines run and produce output. For example, echo "Hello" prints Hello, even if followed by a comment. Comments help explain code without affecting what PHP does.