Programming PHP

Because all operators are required to return a value, the assignment operator returns
the value assigned to the variable. For example, the expression $a = 5 not only assigns
5 to $a, but also behaves as the value 5 if used in a larger expression. Consider the
following expressions:
$a = 5;
$b = 10;
$c = ($a = $b);
The expression $a=$bis evaluated first, because of the parentheses. Now, both $a and
$b have the same value, 10. Finally, $c is assigned the result of the expression $a = $b,
which is the value assigned to the lefthand operand (in this case, $a). When the full
expression is done evaluating, all three variables contain the same value, 10.
Assignment with operation
In addition to the basic assignment operator, there are several assignment operators
that are convenient shorthand. These operators consist of a binary operator followed
directly by an equals sign, and their effect is the same as performing the operation
with the operands, then assigning the resulting value to the lefthand operand.
These assignment operators are:
Plus-equals (+=)
Adds the righthand operand to the value of the lefthand operand, then assigns
the result to the lefthand operand. $a += 5 is the same as $a=$a+5.
Minus-equals (–=)
Subtracts the righthand operand from the value of the lefthand operand, then
assigns the result to the lefthand operand.
Divide-equals (/=)
Divides the value of the lefthand operand by the righthand operand, then assigns
the result to the lefthand operand.
Multiply-equals (*=)
Multiplies the righthand operand with the value of the lefthand operand, then
assigns the result to the lefthand operand.
Modulus-equals (%=)
Performs the modulus operation on the value of the lefthand operand and the
righthand operand, then assigns the result to the lefthand operand.
Bitwise-XOR-equals (^=)
Performs a bitwise XOR on the lefthand and righthand operands, then assigns
the result to the lefthand operand.
Bitwise-AND-equals (&=)
Performs a bitwise AND on the value of the lefthand operand and the righthand
operand, then assigns the result to the lefthand operand.
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