if / then語(yǔ)句后面可以有一個(gè)可選的else語(yǔ)句，當(dāng)布爾表達(dá)式為false時(shí)執(zhí)行。

語(yǔ)法

if expr then
   expr
else
   expr

流程圖

例子

let a : int32 = 100

(* check the boolean condition using if statement *)

if (a < 20) then
   printfn "a is less than 20\n"
else
   printfn "a is not less than 20\n"
   printfn "Value of a is: %d" a

當(dāng)編譯和執(zhí)行程序時(shí)，它會(huì)產(chǎn)生以下輸出 -

a is not less than 20

Value of a is: 100