PHP has nine predefined constants that change value depending on where they are used, also called the “magic constants”.
These magic constants are written with a double underscore at the start and the end, except for the ClassName::class constant.
Constants are like variables, except that once they are defined they cannot be changed or undefined.
A constant is an identifier (name) for a simple value. The value cannot be changed during the script.
A valid constant name starts with a letter or underscore (no $ sign before the constant name).
Note: Unlike variables, constants are automatically global across the entire script.
PHP has a set of math functions that allows you to perform mathematical tasks on numbers.
The pi() function returns the value of PI:
echo(pi());
Sometimes you need to change a variable from one data type into another, and sometimes you want a variable to have a specific data type. This can be done with casting.
Casting in PHP is done with these statements:
(string) – Converts to data type String(int) – Converts to data type Integer(float) – Converts to data type Float(bool) – Converts to data type Boolean(array) – Converts to data type Array(object) – Converts to data type Object(unset) – Converts to data type NULLIn this chapter we will look in depth into Integers, Floats, and Number Strings.
There are three main numeric types in PHP:
IntegerFloatNumber StringsIn addition, PHP has two more data types used for numbers:
InfinityNaNVariables of numeric types are created when you assign a value to them:
$a = 5;
$b = 5.34;
$c = "25";
To insert characters that are illegal in a string, use an escape character.
An escape character is a backslash \ followed by the character you want to insert.
An example of an illegal character is a double quote inside a string that is surrounded by double quotes: Continue reading PHP – Escape Characters
You can return a range of characters by using the substr() function.
Specify the start index and the number of characters you want to return.
Start the slice at index 6 and end the slice 5 positions later:
$x = "Hello World!";
echo substr($x, 6, 5);
Note The first character has index 0.
To concatenate, or combine, two strings you can use the . operator:
$x = "Hello";
$y = "World";
$z = $x . $y;
echo $z;
The result of the example above is HelloWorld, without a space between the two words. Continue reading PHP – Concatenate Strings
PHP has a set of built-in functions that you can use to modify strings.
The strtoupper() function returns the string in upper case:
$x = "Hello World!";
echo strtoupper($x);
A string is a sequence of characters, like “Hello world!”.
Strings in PHP are surrounded by either double quotation marks, or single quotation marks. Continue reading PHP Strings