Programming PHP

The division and multiplication operators have the same precedence, but the result
of the expression depends on which operation we do first:
2/(2*2) // 0.5
(2/2)*2 // 2
The division and multiplication operators are left-associative; this means that in
cases of ambiguity, the operators are evaluated from left to right. In this example, the
correct result is 2.
Implicit Casting
Many operators have expectations of their operands—for instance, binary math
operators typically require both operands to be of the same type. PHP’s variables can
store integers, floating-point numbers, strings, and more, and to keep as much of the
type details away from the programmer as possible, PHP converts values from one
type to another as necessary.
The conversion of a value from one type to another is called casting. This kind of
implicit casting is called type juggling in PHP. The rules for the type juggling done by
arithmetic operators are shown in Table 2-4.
Table 2-4. Implicit casting rules for binary arithmetic operations
Type of first operand Type of second operand Conversion performed
Integer Floating point The integer is converted to a floating-point number
Integer String The string is converted to a number; if the value after conversion is a
floating-point number, the integer is converted to a floating-point
number
Floating point String The string is converted to a floating-point number
Some other operators have different expectations of their operands, and thus have
different rules. For example, the string concatenation operator converts both operands
to strings before concatenating them:
3 . 2.74 // gives the string 32.74
You can use a string anywhere PHP expects a number. The string is presumed to
start with an integer or floating-point number. If no number is found at the start of
the string, the numeric value of that string is 0. If the string contains a period (.) or
upper- or lowercase e, evaluating it numerically produces a floating-point number.
For example:
"9 Lives" – 1; // 8 (int)
"3.14 Pies" * 2; // 6.28 (float)
"9 Lives." – 1; // 8 (float)
"1E3 Points of Light" + 1; // 1001 (float)
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Expressions and Operators | 37