- 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, Decimal. A Boolean counts as an Integer, a String as a Double — two String expressions are converted to numbers and subtracted — and a LongPtr as a Long in a 32-bit build or a LongLong in a 64-bit build. The following are exceptions:
| If | Then result is |
|---|---|
| Subtraction involves a Single and a Long or LongLong | Converted to a Double. |
| result is a Long, LongLong, 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 except Decimal | A Date. |
| Subtraction involves two Date expressions | A Double. |
A declared (non-Variant) result that overflows raises error 6, Overflow. 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.
The rules for every arithmetic operator are collected under Result types and promotion.
Note
LongLong and Decimal take part in subtraction in every twinBASIC build: LongLong exists in 32-bit builds as well, and Decimal can be a declared type, so a declared Decimal on either side gives a declared Decimal. VBA has LongLong only in 64-bit builds, and Decimal only inside a Variant.
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.