new files

Task/Caesar-cipher/Fortran/caesar-cipher.f

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+program Caesar_Cipher
+  implicit none
+
+  integer, parameter :: key = 3
+  character(43) :: message = "The five boxing wizards jump quickly"
+
+  write(*, "(2a)") "Original message  = ", message
+  call encrypt(message)
+  write(*, "(2a)") "Encrypted message = ", message
+  call decrypt(message)
+  write(*, "(2a)") "Decrypted message = ", message
+
+contains
+
+subroutine encrypt(text)
+  character(*), intent(inout) :: text
+  integer :: i
+
+  do i = 1, len(text)
+    select case(text(i:i))
+      case ('A':'Z')
+        text(i:i) = achar(modulo(iachar(text(i:i)) - 65 + key, 26) + 65)
+      case ('a':'z')
+        text(i:i) = achar(modulo(iachar(text(i:i)) - 97 + key, 26) + 97)
+    end select
+  end do
+end subroutine
+
+subroutine decrypt(text)
+  character(*), intent(inout) :: text
+  integer :: i
+
+  do i = 1, len(text)
+    select case(text(i:i))
+      case ('A':'Z')
+        text(i:i) = achar(modulo(iachar(text(i:i)) - 65 - key, 26) + 65)
+      case ('a':'z')
+        text(i:i) = achar(modulo(iachar(text(i:i)) - 97 - key, 26) + 97)
+    end select
+  end do
+end subroutine
+
+end program Caesar_Cipher