Control flow statement for conditional branching

If expression Then [statement(s)] [Else [statement(s)]] [End If]
If expression Then : [statement(s)] [Else [statement(s)]] : End If
If expression Then
[ Elseif expression Then ]
[ Else ]
End If

Remark: EndIf (without blank) is also supported like in QB for backward compatibility.

If...Then is a way to make decisions.
It is a mechanism to execute code only if a condition is true, and can provide alternative code to execute based on more conditions:
  • Execute code (just behind Then) if a condition is true.
  • Execute certain code (just behind Then) if a condition is true and execute other (just behind Else) if it's false.
  • Test other conditions (with Elseif) if the first condition is false.

expression can be one of several forms:
  • a conditional expression, for example:
  • x = 5
  • multiple conditions separated by logical bit-wise operators, for example:
  • x >= 5 And x <= 10
  • multiple conditions separated by logical short-circuit operators, for example:
  • y <> 0 AndAlso x \ y = 1
    (in this case, "x \ y = 1" will only be evaluated if "y <> 0" is True)
  • any numerical expression, in which case a value of zero (0) represents False, and a non-zero value represents True

Both multi-line and single-line Ifs can be nested. In the latter case, the optional End Ifs can be useful to control where nested Ifs begin and end.

The multi-line syntax allows several Elseifs (but none after a Else) and tests can be nested (there must be in this case as many End Ifs as Ifs).
If the condition of the If is not true, those of Elseifs blocks are tested in succession:
  • If either of these is true, the corresponding code is executed, then the program skips the following blocks to continue after the End If.
  • If none are true, the code following the Else (if exists) is executed alone.

In the -lang fb and -lang fblite dialects, colons (:) can be used instead of newlines to construct multi-line If blocks on a single line.

Note: The single-line syntax If...Goto, as shortcut for If...Then Goto, is deprecated and it only exists for compatibility with QB.

'' Here is a simple "compute the square root" code using a single-line if...then for the decision,
'' but with multiple statements extended with colons (:)

Dim As Double d , r
r = -1
d = 2
'd = -3

If d > 0 Then r = Sqr(d) : Print "square root computed:" Else r = 0 : Print "square root not computed:"
Print r


'' Here is a simple "guess the number" game using a multi-line if...then for a decision.

Dim As Integer num, guess

num = Int(Rnd * 10) + 1 'Create a random number between 1 and 10...
Print "guess the number between 1 and 10 (or CTRL-C to abort)"

Do 'Start a loop

    Input "Guess"; guess 'Input a number from the user

    If guess > 10 OrElse guess < 1 Then  'The user's guess is out of range
        Print "The number can't be greater then 10 or less than 1!"
    ElseIf guess > num Then  'The user's guess is too high
        Print "Too high"
    ElseIf guess < num Then  'The user's guess is too low
        Print "Too low"
    Else                     'The user guessed the right number!
        Print "Correct!"
        Exit Do   'Exit the loop
    End If

Loop 'Go back to the start of the loop


Dialect Differences:
Differences from QB:
See also:
Back to Control Flow
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