In the previous section you learned about variables, data type, and constant and
how to declare them. However, to use or declare variables or constants you need
operators. The fallowing problem and its solution explain the use of operators.
Identify the operators to be used
Operators are an integral part of any programming language, they are symbol
that represent a specific action. For an example, the plus sign indicates that
addition needs to be performed and is an operator use for addition. Using
operators, you can perform a number of operation on a variable:

Assign a value to a variable

Change the value of a variable

Compare two or more values

Specify a condition
There are 6 basic operator categories:

Arithmetic Operator

Assignment Operator

Comparison Operator

Increment/decrement Operator

String Operator

Logical Operator
Arithmetic operators
Arithmetic operators are used to perform elementary mathematical calculation and
are used when value of variable declare in integer type.
Name 
Example 
Output 
Addition 
$a+$b 
The sum of $a and $b 
Subtraction 
$a$b 
The difference between $a and $b 
Multiplication 
$a*$b 
The product of $a and $b 
Division 
$a/$b 
The quotient of $a and $b 
Modules 
$a%$b 
The remainder after dividing $a and $b 
Let us look at some examples for a better understanding of arithmetic operators:
Addition
$a = 3;
$b = 6;
$c = $a+$b ; // The value of $c is now 9.
Subtraction
$a = 11;
$b = 2;
$c = $a$b; //The value of $c is now 9.
Multiplication
$a = 3;
$b = 3;
$c = $a*$b; //The value of $c is now 9.
Division
$a = 18;
$b = 2;
$c = $a/$b ; //The value of $c is 9.
Modules
$a = 9;
$b = 3;
$c = $a%$b; //The value of $c is now 0.
Assignment Operators
Assignment operators are use to assign a specific value to variable. They are also
use to change the existing value of a variable by adding or subtracting from
the variable 's current value. A few examples are =, +=, = and .=.
In PHP you can use more than one assignment operator in a single statement, as
shown below:
$a = ($b=4) + ($c=5);
The variable $a, $b and $c are now integer types and will hold the values 9, 4 and
5, respectively.
Operator 
Usage 
Output 
= (equal to) 
$a = 9; 
Assign value 9 to variable $a; 
+= (plus equal to) 
$a += 9; 
Adds the original value assign to the variable $a to 9. Now the value of
$a will be 9. 
= (minus equal to) 
$a += 3; 
Subtract the number specified from the original value of $a. Now the
value of $a will be 6. 
.= (dot equal to) 
$a .=" new numbers."; 
(add) the new value specified with the original value of the variable.
Now the value of $a will be 9 new numbers. 