ブール演算子 (式言語)

2 つのオペランドと 1 つのブール演算子で構成される式は、式が真の場合は True に評価され、式が偽の場合は False に評価されます。ただし、オペランドの一方が NULL の場合は、演算子とオペランドの種類により、結果は True、False、NULL のいずれかになります。可能な組み合わせは次のとおりです。

ブール演算子を含む数式の一方のオペランドが NULL の場合は、次の場合を除いて、式全体が NULL に評価されます。

• 演算子が AND で他のオペランドが False の場合は、式は False に評価されます。
• 演算子が OR で他のオペランドが True の場合は、式は True に評価されます。
• 演算子が IMP で第 1 オペランドが False の場合は、式は True に評価されます。
• 演算子が IMP で第 2 オペランドが True の場合は、式は True に評価されます。

次の例では、1 から 10 までの 2 つの整数をユーザーが入力し、最初の数値 (num1%) が 6 より小さいかどうか、そして 2 番目の値 (num2%) が 5 より大きいかどうかをテストします。次にこの 2 つのテストの真の値に基づいてメッセージを表示します。

Dim num1 As Integer
Dim num2 As Integer 
num1% = InputBox("Enter an integer between 1 and 10:")
num2% = InputBox("Enter an integer between 1 and 10:")
Print "num1 = " & num1% & " num2 = " & num2%
If num1% <6 And num2% >5 Then 
   Print "And:" & num1% & " is less than 6 and " & num2% & _
      " is greater than 5."
End If
If num1% <6 Or num2% >5 Then
   Print "Or:" & num1% & " is less than 6 or " & num2% & _  
      " is greater than 5, or both."
End If
If num1% <6 XOr num2% >5 Then
   Print "XOr: " & num1% & " is less than 6 or " & num2% & _
      " is greater than 5, but not both."
End If
If num1% <6 Eqv num2% >5 Then
   Print "Eqv:" & num1% & " is less than 6 and " & num2% & _
      " is greater than 5, or " & num1% & _
      " is greater than 5 and " & num2% & " is less than 6."
End If
If num1% <6 Imp num2% >5 Then 
   Print "Imp:" & num1% & " is less than 6 and " & num2% & _
      " is greater than 5, or " & num1% & _
      " is greater than 5 and " & num2% & _
      " is less than 6, or " & num1% &  _
      " is greater than 5 and " & num2% & _
      " is greater than 5."
End If
' Sample Output:
' num1 = 6 num2 = 6 
' Or: 6 is less than 6 or 6 is greater than 5, or both.
' XOr: 6 is less than 6 or 6 is greater than 5, but not both.
' Imp: 6 is less than 6 and 6 is greater than 5, or 6 is 
' greater than 5 and 6 is less than 6, or 6 
' is greater than 5 and 6 is greater than 5.

' num1 = 10 num2 = 1 
' Eqv: 10 is less than 6 and 1 is greater than 5, or 10
' is greater than 5 and 1 is less than 6.
' Imp: 10 is less than 6 and 1 is greater than 5, or 10 is
' greater than 5 and 1 is less than 6, or 
' 10 is greater than 5 and 1 is greater than 5.

' num1 = 5 num2 = 9 
' And: 5 is less than 6 and 9 is greater than 5.
' Or: 5 is less than 6 or 9 is greater than 5, or both.
' Eqv: 5 is less than 6 and 9 is greater than 5, or 5
' is greater than 5 and 9 is less than 6.
' Imp: 5 is less than 6 and 9 is greater than 5, or 5 is
' greater than 5 and 9 is less than 6, or 
' 5 is greater than 5 and 9 is greater than 5.