Fortran關係運算子 - tw511教學網

下表列出了所有的Fortran支援的關係運算子。假設變數A=10和變數B=20，則：

操作符	等同	描述	範例
==	.eq.	檢查兩個運算元的值相等與否，如果是，則條件變為真。	(A == B) i不為 true.
/=	.ne.	檢查，兩個運算元的值相等與否，如果值不相等，則條件變為真。	(A != B) 為 true.
>	.gt.	檢查，左運算元的值大於右運算元的值，如果是的話那麼條件為真。	(A > B)不為true.
<	.lt.	檢查，左運算元的值是否小於右運算元的值，如果是的話那麼條件為真。	(A < B) 是 true.
>=	.ge.	檢查，左邊的運算元的值是否大於或等於右運算元的值，如果是，則條件變為真。	(A >= B) 不為 true.
<=	.le.	檢查，左邊的運算元的值是否小於或等於右運算元的值，如果是，則條件變為真。	(A <= B) 為 true.

範例

試試下面的例子就明白所有在Fortran語言可用的邏輯運算子：

program logicalOp

! this program checks logical operators
implicit none  

   ! variable declaration
   logical :: a, b
   
   ! assigning values 
   a = .true.   
   b = .false. 
   
   if (a .and. b) then
      print *, "Line 1 - Condition is true"
   else
      print *, "Line 1 - Condition is false"
   end if
   
   if (a .or. b) then
      print *, "Line 2 - Condition is true"
   else
      print *, "Line 2 - Condition is false"
   end if
          
   ! changing values 
   a = .false.   
   b = .true. 
   
   if (.not.(a .and. b)) then
      print *, "Line 3 - Condition is true"
   else
      print *, "Line 3 - Condition is false"
   end if
   
   if (b .neqv. a) then
      print *, "Line 4 - Condition is true"
   else
      print *, "Line 4 - Condition is false"
   end if
   
   if (b .eqv. a) then
      print *, "Line 5 - Condition is true"
   else
      print *, "Line 5 - Condition is false"
   end if
   
end program logicalOp

當編譯並執行上述程式,將產生以下結果：

Line 1 - Condition is false
Line 2 - Condition is true
Line 3 - Condition is true
Line 4 - Condition is true
Line 5 - Condition is false