Float type and precision in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP float addition?

Consider the following PHP code:

$a = 0.1 + 0.2;
echo $a === 0.3 ? 'Equal' : 'Not equal';

What will be printed?

PHP

$a = 0.1 + 0.2;
echo $a === 0.3 ? 'Equal' : 'Not equal';

A Not equal

B Equal

C 0.3

D Error

💡 Hint

Think about how floating point numbers are stored in computers.

Due to floating point precision, 0.1 + 0.2 is not exactly 0.3 in PHP, so the strict comparison fails and 'Not equal' is printed.

❓ Predict Output

intermediate

What is the output of this float formatting code?

What does this PHP code output?

$num = 1.23456789;
echo number_format($num, 4);

PHP

$num = 1.23456789;
echo number_format($num, 4);

A 1.2346

B 1.2345

C 1.23456789

D 1.234

💡 Hint

number_format rounds the number to the specified decimals.

number_format rounds the number to 4 decimal places, so 1.23456789 becomes 1.2346.

🔧 Debug

advanced

Why does this float comparison fail?

Examine this PHP code snippet:

$x = 0.15 + 0.15;
$y = 0.1 + 0.2;
if ($x == $y) {
    echo 'Equal';
} else {
    echo 'Not equal';
}

Why does it print 'Not equal'?

PHP

$x = 0.15 + 0.15;
$y = 0.1 + 0.2;
if ($x == $y) {
    echo 'Equal';
} else {
    echo 'Not equal';
}

A Because both sums are exactly equal but the code has a syntax error

B Because 0.1 + 0.2 is exactly 0.3 but 0.15 + 0.15 is not

C Because PHP does not support float addition

D Because 0.15 + 0.15 is exactly 0.3 but 0.1 + 0.2 is not

💡 Hint

Try printing the values of $x and $y with high precision.

0.15 + 0.15 equals exactly 0.3 in floating point, but 0.1 + 0.2 does not due to precision errors, so the comparison fails.

📝 Syntax

advanced

Which option causes a syntax error with float literals?

Which of the following PHP code snippets will cause a syntax error?

A $num = 0.5;

B $num = 1.2e3;

C $num = 1.2.3;

D $num = 2e-2;

💡 Hint

Look carefully at the float literal formats.

Option C has two decimal points in the number literal, which is invalid syntax in PHP.

🚀 Application

expert

How many items are in the array after float keys are used?

What is the number of elements in this PHP array?

$arr = [];
$arr[1.0] = 'a';
$arr[1.00] = 'b';
$arr[1.000] = 'c';
echo count($arr);

PHP

$arr = [];
$arr[1.0] = 'a';
$arr[1.00] = 'b';
$arr[1.000] = 'c';
echo count($arr);

A Error

B 1

C 3

D 0

💡 Hint

Think about how PHP treats float keys in arrays.

PHP converts float keys to integers when used as array keys, so all keys become 1, overwriting previous values. The array has 1 element.