VisaSpark
Sign in
beginner18 min

Variables, Types, and String Interpolation

PHP's `$variable` syntax, loose typing, and interpolating values into strings.

What you'll learn

  • Declare a variable using PHP's `$` sigil
  • Distinguish single-quoted (literal) strings from double-quoted (interpolating) strings
  • Predict how PHP's loose typing handles arithmetic and concatenation involving numeric strings

Explanation

Every PHP variable name starts with a $ sigil: $age = 30;. Unlike some languages, you never declare a variable's type up front -- PHP figures it out from the assigned value, and a variable can hold a different type later if you reassign it (this is PHP's loose typing; you can opt into stricter behavior per-file with declare(strict_types=1);, which mainly affects function argument/return type coercion rather than variable assignment itself).

PHP has two everyday string quoting styles that behave differently: a single-quoted string ('Hello, $name') is almost entirely literal -- $name stays as the literal text $name, not the variable's value. A double-quoted string ("Hello, $name") interpolates -- it substitutes the variable's actual value directly into the string, and also recognizes escape sequences like \n.

PHP's loose typing extends to numeric strings: a string that looks like a number, such as "85", can be used directly in arithmetic -- "85" + 10 evaluates to the integer 95, with PHP converting the string to a number first. This is different from the . (dot) concatenation operator, which always converts its operands to strings and joins them -- "85" . 10 produces the string "8510", not a sum.

Getting + (arithmetic, numeric coercion) and . (concatenation, string coercion) confused is one of the most common early PHP mistakes, especially coming from a language like JavaScript where + does both jobs depending on the operand types.

Guided lab

Predict: Loose typing with numeric strings

PHPNot executed
This lab does not run in your browser or on VisaSparkSchools's servers. Read the code, predict what it does, then reveal the real expected output.

Read this script and predict exactly what it sends to the browser.

<?php
$name = "Ada";
$age = 30;
$score = "85";
$bonus = 10;

echo "$name is $age years old.\n";
echo "Total score: " . ($score + $bonus) . "\n";
echo "Score as string: " . $score . $bonus . "\n";

Stuck? Get a hint.

Common mistakes

  • Forgetting the `$` sigil and writing a bare identifier where PHP expects a variable name.
  • Using a single-quoted string when interpolation was intended, then being confused why `'Hello, $name'` prints the literal text `$name` instead of its value.
  • Confusing `+` (numeric addition, converting operands to numbers) with `.` (string concatenation, converting operands to strings) -- they are not interchangeable the way JavaScript's `+` can be.

Knowledge check

Knowledge check

1. What sigil must precede every PHP variable name?
2. In `'Hello, $name'` (single quotes), what does PHP do with `$name`?
3. What does the expression `"85" + 10` evaluate to in PHP?

Takeaway

Use double-quoted strings when you want variable interpolation, and remember `+` coerces to numbers while `.` coerces to strings for concatenation.

Summary

PHP variables use a `$` sigil and are loosely typed; double-quoted strings interpolate values and escape sequences, single-quoted strings don't; `+` and `.` coerce operands differently.

References

Your notes

Notes save automatically.

Finished this lesson?

Mark it complete to track your progress and schedule a future review.

Next: Control Flow: if, foreach, while, and match →