Variable declaration with dollar sign in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code with variable variables?

Consider the following PHP code snippet. What will it output?

PHP

<?php
$a = 'hello';
$hello = 'world';
echo $$a;
?>

A $hello

B hello

C world

D Error: Undefined variable

💡 Hint

Remember that $$a means the variable whose name is the value of $a.

The variable $a contains the string 'hello'. So $$a means $hello, which contains 'world'. Thus, echo $$a outputs 'world'.

❓ Predict Output

intermediate

What will this PHP code output?

Analyze the following PHP code and select the output it produces.

PHP

<?php
$var = 'name';
$name = 'PHP';
echo "$var is $name";
?>

A PHP is name

B name is PHP

C $var is $name

D Error: Undefined variable

💡 Hint

Variables inside double quotes are replaced by their values.

Inside double quotes, $var and $name are replaced by their values 'name' and 'PHP' respectively. So the output is 'name is PHP'.

❓ Predict Output

advanced

What error does this PHP code raise?

Examine the code below. What error will it produce when run?

PHP

<?php
$1var = 'test';
echo $1var;
?>

A Parse error: syntax error, unexpected '1var'

B Notice: Undefined variable: 1var

C Fatal error: Cannot use numeric variable name

D test

💡 Hint

Variable names in PHP cannot start with a number.

PHP variable names must start with a letter or underscore. Starting with a number causes a syntax error.

❓ Predict Output

advanced

What is the output of this PHP code using variable variables and concatenation?

What will this PHP code print?

PHP

<?php
$foo = 'bar';
$bar = 'baz';
$baz = 'qux';
echo $$$foo;
?>

A qux

B Error: Undefined variable

C bar

D baz

💡 Hint

Evaluate from right to left: $$$foo means ${$foo} then ${${$foo}}.

First, $foo = 'bar', so $$foo = $bar = 'baz'. Then $$$foo = ${$bar} = $baz = 'qux'. So echo $$$foo outputs 'qux'.

🧠 Conceptual

expert

How many variables are declared and accessible after this PHP code runs?

Consider this PHP code snippet. How many distinct variables are declared and accessible after execution?

PHP

<?php
${'var'.'1'} = 10;
$var2 = 20;
$var3 = ${'var'.'2'} + 5;
?>

A 1

B 4

C 2

D 3

💡 Hint

Count all variables with names starting with $var and those created dynamically.

Variables declared: $var1 (via ${'var'.'1'}), $var2, and $var3. So total 3 variables accessible.