4. Scala function basis

I. built-in control structure

1. If expression

Val filenameNice = if (! args.isEmpty) args (0) else "default.txt"

2. While cycle

Whether it's while or do...while, we can't call it an expression, we should call it a loop, because they don't calculate a new value. Their value type is Unit, and Unit and () are equal in scala

Def gcdLoop (x: Long, y: Long): Long = {

Var a = x

Var b = y

While (a! = 0) {

Val temp = a

A = b% a

B = temp

}

B

}

Do...while... Expression.

Var line = ""

Do {

Line = scala.io.StdIn.readLine ()

Println ("Read:" + line)

} while (line! = "")

Reassigning var in scala always returns () (that is, Unit)

()! = "will return true forever

Var tempLine = ""

While ((tempLine = scala.io.StdIn.readLine ())! = ") / / This doesn't work!

Println ("Read:" + tempLine)

Because the while loop does not calculate the value, the while code is not so functional and generally contains the var variable

Scala chose to keep while because the code that uses while in some scenarios is still very readable.

Using recursion to eliminate var

Def gcd (x: Long, y: Long): Long =

If (y = = 0) x else gcd (y, x% y)

3. For expression

Iterate over an arbitrary set with for expression

Val filesHere = (new java.io.File ("."). ListFiles

For (file