(a as number,b as number,c as number) =>
let
    四則運(yùn)算 = if c = 1 then a + b
                else if c = 2 then a - b
                else if c = 3 then a * b
                else if c = 4 then a / b
                else "參數(shù)錯(cuò)誤"
in
    四則運(yùn)算