Scala II process control

1、 Branch control if-else

Examples ： demand 1： demand ： Enter the age , If the age is less than 18 year , The output “ childhood ”. If age is greater than or equal to 18 And less than or equal to 30, The output “ middle-aged ”, otherwise , Output “ The elderly ”

object TestIfElse  {
    def main(args: Array[String]): Unit = {

        println("input age")
        var age = StdIn.readInt()

        if (age < 18){
            println(" childhood ")
        }else if(age>=18 && age<30){
            println(" middle-aged ")
        }else{
            println(" The elderly ")
        }
    }
}

（2） demand 2：Scala in if else An expression actually has a return value , The specific return value depends on the The last line of the code body .

object TestIfElse  {
    def main(args: Array[String]): Unit = {

        println("input age")
        var age = StdIn.readInt()

        val res :String = if (age < 18){
            " childhood "
        }else if(age>=18 && age<30){
            " middle-aged "
        }else{
            " The elderly "
        }

        println(res)
    }
}

（3）Java The ternary operator in can be if else Realization   If braces {} There's only one line of logical code inside , Braces can be omitted . If you omit braces ,if Only works on the nearest line of logic code .

object TestIfElse {

    def main(args: Array[String]): Unit = {

        // Java
// int result = flag?1:0

        // Scala
        println("input age")
        var age = StdIn.readInt()
        val res:Any = if (age < 18)  " childhood " else " adult "
" It doesn't work "

        println(res)
    }
}

2 For Cycle control

2.1 Range data cycle （To） Close back and forth

for(i <- 1 to 3){
    print(i + " ")
}
println()

2.2  Range data cycle （Until） To close before and open after

for(i <- 1 until 3) {
    print(i + " ")
}
println()

2.3  Cycle guard

Cycle guard , That is, circulation protection （ Also known as conditional judgment , The guards ）. The protection type is true Then go inside the circulatory body , by false Then skip , Be similar to continue.

for(i <- 1 to 3 if i != 2) {
    print(i + " ")
}
println()

2.4 Cycle step

demand ： Output 1 To 10 All odd numbers within

for (i <- 1 to 10 by 2) {
    println("i=" + i)
}

2.5 Nested loop

for(i <- 1 to 3; j <- 1 to 3) {
    println(" i =" + i + " j = " + j)
}

2.6  Loop return value

Return the results processed during traversal to a new Vector Collection , Use yield keyword

val res = for(i <- 1 to 10) yield i
println(res)

2.7 Flashback printing

If you want to print a set of data in reverse order , It can be used reverse. 

for(i <- 1 to 10 reverse){
    println(i)
}

3 Cycle break

3.1 Scala Built in control structure, specially Removed break and continue, To better adapt Functional programming , It is recommended to use the functional style to solve break and continue The function of , Not a keyword .Scala Use in breakable Control structure to achieve break and continue function

import scala.util.control.Breaks._

object TestBreak {

    def main(args: Array[String]): Unit = {
    
        breakable {
            for (elem <- 1 to 10) {
                println(elem)
                if (elem == 5) break
            }
        }
    
        println(" Normal end of cycle ")
    }

  Loop traversal 10 All data within , Odd print , Even skip （continue）

object TestBreak {

    def main(args: Array[String]): Unit = {

        for (elem <- 1 to 10) {
            if (elem % 2 == 1) {
                println(elem)
            } else {
                println("continue")
            }
        }
    }
}