# Arithmetic and comparison operators

An operator is used to perform an operator on one or more values. The most common sorts of operators are arithmetic operators, such as those which perform addition or multiplication. For example:

```  process
local integer x

set x to 1 + 1

```

The arithmetic operators available in OmniMark are `+` (addition), `-` (subtraction), `*` (multiplication), `/` (division), and `modulo` (the remainder you get when you divide the number by the base value).

OmniMark also provides a full set of operators that are used to compare two or more numeric values. For example:

```  process
do when x = y
output "equal%n"

else when x > y
output "greater%n"

else when x < y
output "lesser%n"
done
```

The other available numeric comparison operators are != (not equal), `>=` (greater than or equal to), and `<=` (less than or equal to).

Other common operators are `&`, `|`, and `!` (the `and`, `or`, and `not` Boolean operators). These are usually used to create more complex conditions and tests in OmniMark. For example:

```  process
do when x = y & z > 4
output "first test is true%n"

else when y = z | x = 4
output "second test is true%n"

else
output "neither test is true%n"
done
```

### Comparing records

You can compare two record variables using the reference equality operator, `==`.

You can overload OmniMark's arithmetic and comparison operators to work with new data types, particularly types that you define using records, by writing overloaded functions. When you overload a comparison operator, the return type must be `switch`.