Programming PHP

PHP recognizes floating-point numbers written in two different formats. There’s the
one we all use every day:
3.14
0.017
-7.1
but PHP also recognizes numbers in scientific notation:
0.314E1 // 0.314*10 1, or 3.14
17.0E-3 // 17.0*10 -3, or 0.017
Floating-point values are only approximate representations of numbers. For example,
on many systems 3.5 is actually represented as 3.4999999999. This means you
must take care to avoid writing code that assumes floating-point numbers are represented
completely accurately, such as directly comparing two floating-point values
using ==. The normal approach is to compare to several decimal places:
if (int($a * 1000) == int($b * 1000)) {
// numbers equal to three decimal places
Use the is_float( ) function (or its is_real( ) alias) to test whether a value is a floating
point number:
if (is_float($x)) {
// $x is a floating-point number
}
Strings
Because strings are so common in web applications, PHP includes core-level support
for creating and manipulating strings. A string is a sequence of characters of arbitrary
length. String literals are delimited by either single or double quotes:
'big dog'
"fat hog"
Variables are expanded within double quotes, while within single quotes they are
not:
$name = "Guido";
echo "Hi, $name\n";
echo 'Hi, $name';
Hi, Guido
Hi, $name
Double quotes also support a variety of string escapes, as listed in Table 2-2.
Table 2-2. Escape sequences in double-quoted strings
Escape sequence Character represented
\" Double quotes
\n Newline
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