Conditional function that returns one of two values.

IIf ( condition, expr_if_true, expr_if_false )

The condition to test.
A non-zero value evaluates as true, while a value of zero evaluates as false.
An expression to evaluate and return if condition is true.
It must return:
  • a numeric value, which can be an integer, floating point number or a pointer, including Boolean,
  • or a string value,
  • or an UDT value.
An expression to evaluate and return if condition is false.
It must be same type as expr_if_true (either numeric, either string or UDT).

IIf returns a different numeric or string or UDT value (not a reference) depending of the result of a conditional expression evaluated at run-time. Its typical use is in the middle of an expression; it avoids splitting it to put a conditional in the middle.

IIf only evaluates the expression that it needs to return. This saves time, and can also be useful to prevent evaluating expressions that might be invalid depending on the condition.

When IIf treats expressions of mixed numeric types (conditional expression evaluated at run-time):
  • if at least one expression is of floating-point type, the result type is the floating-point type (the bigger in case of two floating-point types),
  • if the two expressions are of integer types, the result type is the bigger type of both (see Coercion and Conversion for the precise ranking of integer types).

Warning: The ability to accept mixed numeric types, strings and UDTs is only supported from the fbc version 0.90.

Dim As Integer a, b, x, y, z
a = (x + y + IIf(b > 0, 4, 7)) \ z
is equivalent to:
Dim As Integer a, b, x, y, z, temp
If b > 0 Then temp = 4 Else temp = 7
a = (x + y + temp) \ z

Dim As Integer I
I = -10
Print I, IIf(I>0, "positive", IIf(I=0, "null", "negative"))
I = 0
Print I, IIf(I>0, "positive", IIf(I=0, "null", "negative"))
I = 10
Print I, IIf(I>0, "positive", IIf(I=0, "null", "negative"))

Type UDT1
  Dim As Integer I1
End Type

Type UDT2 Extends UDT1
  Dim As Integer I2
End Type

Dim As UDT1 u1, u10 = (1)
Dim As UDT2 u2, u20 = (2, 3)

u1 = IIf(0, u10, u20)
Print u1.I1
u1 = IIf(1, u10, u20)
Print u1.I1

u2 = IIf(0 , u10, u20)
Print u2.I1; u2.I2
'u2 = Iif(1, u10, u20) ''Invalid assignment/conversion

Dialect Differences:
Differences from QB:
See also:
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