TopolearnWeb code is mostly string handling: building HTML, parsing input, formatting output.
Single-quoted strings are literal: 'Hello $name\n' prints exactly that. Double-quoted strings interpolate variables and understand escapes like \n and \t. Use braces for anything more than a plain variable: "Hi {$user['name']}" or "{$order->total}".
For multi-line text use heredoc (<<<EOT ... EOT;), which interpolates like double quotes, or nowdoc (<<<'EOT'), which is literal. Since PHP 7.3 the closing marker may be indented, and that indentation is removed from every line.
Join strings with . and append with .=. Useful functions:
str_contains,str_starts_with,str_ends_with(PHP 8) for simple checks.strtoupper,trim,str_replace,substr,explode,implode,str_pad.sprintf('%05.2f', $x)andnumber_formatfor formatting.
PHP strings are byte arrays, not character arrays. strlen('héllo') is 6 because é takes two bytes in UTF-8. For text in human languages use the mbstring functions: mb_strlen, mb_substr, mb_strtoupper. PHP 8.4 added mb_trim and mb_ucfirst.
Strings can be indexed: $s[0] is the first byte, and $s[-1] the last.
Example
<?php
$name = 'Zoë';
$items = ['tea', 'cake'];
echo 'Hi $name', "\n"; // Hi $name
echo "Hi $name, {$items[1]}\n"; // Hi Zoë, cake
$text = <<<TXT
Order for $name:
- {$items[0]}
TXT;
echo $text, "\n"; // indentation of the closing marker is stripped
echo strlen($name), " ", mb_strlen($name), "\n"; // 4 3
echo implode(', ', $items), "\n"; // tea, cake
var_dump(str_contains('hello', 'ell')); // bool(true)
printf("%-6s|%06.2f\n", 'total', 3.14159); // total |003.14Remember
- Single quotes are literal; double quotes and heredoc interpolate
- Use {$expr} for array elements and properties inside strings
- strlen counts bytes; use mb_* functions for characters
Watch out for
- Using substr or strlen on UTF-8 user text and cutting a multi-byte character in half.