運算子優先順序

當表示式中有多個運算時，每個部分都會依照預先定義的順序 (稱為運算子優先順序) 進行評估與解析。您可以使用括號來置換優先順序，強制先評估表示式的某些部分，再評估其他部分。括號內的運算一律會在括號外的運算之前執行。不過，在括號內仍會維持標準運算子優先順序。

當表示式中包含多個類別的運算子時，會先評估算術運算子，接著評估比較運算子，最後評估邏輯運算子。所有比較運算子的優先順序都相同，亦即，它們會依照出現的順序，從左到右依序評估。算術運算子與邏輯運算子的評估順序如下。

下列範例說明運算子程序的用法：

範例 1：

Dim Result
Result = 2 + 3 * 4   ' Multiplication is performed first.
'Result has value 14
Result = (2 + 3) * 4   ' Parentheses override precedence.
'Result has value 20

範例 2：

Dim A, B, C
A = 5
B = 10
C = 20
Dim ComparisonResult
ComparisonResult = A + B > C / 2   ' Division is performed first, then addition, then comparison.
'ComparisonResult   Outputs: True (10 / 2 = 5, then 5 + 5 = 10, 10 > 10 is False, but corrected if comparison operator order is properly enforced)

ComparisonResult = (A + B) > (C / 2)   ' Parentheses enforce precedence.
'ComparisonResult Outputs: True (15 > 10)

範例 3：

Dim X, Y, Z
X = 5
Y = 10
Z = 15

Dim LogicalResult
LogicalResult = X + Y > Z And X < Y   ' Addition and comparison are performed first, then logical AND.
'LogicalResult Outputs: False (10 + 5 > 15 is False, and 5 < 10 is True, False And True is False)

LogicalResult = (X + Y > Z) And (X < Y)   ' Parentheses enforce precedence.
'LogicalResult Outputs: False (still False And True)

範例 4：

Dim NestedResult
NestedResult = (2 + (3 * 4)) * 5   ' Inner parentheses are evaluated first, then outer.
'NestedResult Outputs: 70 (3 * 4 = 12, 2 + 12 = 14, 14 * 5 = 70)

範例 5：

Dim A, B, C
A = 5
B = 2
C = 10
Dim ClearResult
ClearResult = (A * B) + (C / A)   'Using parentheses to make the expression clear.
'ClearResult Outputs: 12 (5 * 2 = 10, 10 / 5 = 2, 10 + 2 = 12)

請參閱 BSL 運算子以取得算術、比較和邏輯運算子的完整指南。