- and -= operators
Used to find the difference between two numbers, or to indicate the negative value of a numeric expression. The compound form -= subtracts-and-assigns in one step.
Syntax:
result = number1 - number2
- number
variable -= number (twinBASIC)
- result
- Any numeric variable.
- variable
- (twinBASIC) Any numeric variable or writable property.
- number, number1, number2
- Any numeric expressions.
In the binary form, - is the arithmetic subtraction operator that returns the difference between number1 and number2. In the unary form, - is the negation operator that returns the negative of number.
The data type of result is usually the same as that of the most precise expression. The order of precision, from least to most precise, is Byte, Integer, Long, LongLong, Single, Double, Currency. The following are exceptions:
| If | Then result is |
|---|---|
| Subtraction involves a Single and a Long | Converted to a Double. |
| result is a Long, Single, or Date variant that overflows its legal range | Converted to a Variant containing a Double. |
| result is a Byte variant that overflows its legal range | Converted to an Integer variant. |
| result is an Integer variant that overflows its legal range | Converted to a Long variant. |
| Subtraction involves a Date and any other data type | A Date. |
| Subtraction involves two Date expressions | A Double. |
If one or both expressions are Null expressions, result is Null. If an expression is Empty, it is treated as 0.
Note
The order of precision used by addition and subtraction is not the same as the order of precision used by multiplication.
Compound assignment
x -= y is the twinBASIC shorthand for x = x - y. The left-hand side is evaluated once; the result follows the same type-promotion and Null / Empty rules described above. -= is a statement, not an expression — it does not produce a value.
Dim Total As Long = 100
Total -= 5 ' Total is now 95.
Total -= 5 ' Total is now 90.
Example
This example uses the - operator to calculate the difference between two numbers.
Dim MyResult
MyResult = 4 - 2 ' Returns 2.
MyResult = 459.35 - 334.90 ' Returns 124.45.
MyResult = -MyResult ' Unary negation: returns -124.45.