Scala-day03- operators and loop control

One ： Arithmetic operator

        1： Basic grammar

        For division marks , There is a difference between integer division and decimal division , Divide integers , Keep only the integer parts , And discard the decimal part .

        Modulo for a number a%b, and Java As like as two peas .

        2： Case study

package chapter03

object TestArithmetic {
  def main(args: Array[String]): Unit = {
    var r1:Int = 10/3 //3
    println("r1=" + r1)

    var r2:Double = 10 / 3  //3.0
    println("r2=" + r2)

    var r3:Double = 10.0  / 3 //3.3.333
    println("r3=" + r3)
    println("r3=" + r3.formatted("%.2f")) // Keep the decimal point 2 position , Use rounding 

    var r4 = 10 % 3 //1
    println("r4=" + r4)
  }
}

Two ： Relational operator

        1： Basic grammar

        2.1： Case study 1

package chapter03

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

    var a:Int = 2
    var b:Int = 1

    println(a > b)  //true
    println(a >= b)   //true
    println(a <= b)   //false
    println(a < b)    //false
    println("a==b" + (a == b))  //false
    println(a != b)   //true
  }
}

        2.2： Case study 2

        java in ：== Compare the values of the two variables themselves , That is, the addresses of two objects in memory

                        equals Compare whether the contents contained in the string are the same

public static void main(String[] args) {
    String s1 = "abc";
    String s2 = new String("abc");
    System.out.println(s1 == s2);
    System.out.println(s1.equals(s2));
}
 Output   result ：
false
true

        Scala：== More similar to Java Medium equals

def main(args: Array[String]): Unit = {
    val s1 = "abc"
    val s2 = new String("abc")
    println(s1 == s2)
    println(s1.eq(s2))
}
 Output   result ：
true
false

3、 ... and ： Logical operators

        1： Basic grammar , hypothesis A by true,B by false

        2： Case study

package chapter03

object TestLogic {
  def main(args: Array[String]): Unit = {
    var a = true
    var b = false

    println("a&&b=" + (a&&b))   //false
    println("a||b=" + (a || b))   //true
    println("!(a&&b)" + (!(a && b)))  //false
  }
}

Four ： Assignment operator

        1： Basic grammar ：Scala There is no ++、-- The operator , Can pass +=、-= To achieve the same effect

         

        2： Case study

object TestAssignment {
    def main(args: Array[String]): Unit = {
        var r1 = 10
        r1 += 1 //  No, 
        r1 -= 2 //  No, 
    }
}

5、 ... and ： An operator

        1： Basic grammar ：a：60,b：13

         2： Case study

object TestPosition {
    def main(args: Array[String]): Unit = {
        //  test ： 1000 << 1 =>10000
        var n1 :Int =8
        n1 = n1 << 1
        println(n1)
    }
}

6、 ... and ： Conditional branch

        1： Single branch

if ( Conditional expression ) {

        Execute code block

}

        2： Double branch

if （ Conditional expression ） {

        Execute code block 1

} else {

        Execute code block 2

}

        3： Multiple branches

if （ Conditional expression 1） {

        Execute code block 1

} else if ( Execute expression 2) {

        Execute code block 2

}...

else {

        Execute code block n

}

         4： Nesting branches

if （） {

        if （）{

        }else{

        }

}

7、 ... and ：FOR loop

         1： Range data cycle （To）

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

//1.i The variable representing the loop ,<-  Regulations to
//2.i Will be from 1-3 loop , Close back and forth 

        2： Range data cycle （Unitl）

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

//1. The difference between this method and the previous one is i It's from 1 To 3-1
//2. Front closed back open return 

        3： Cycle guard

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

println()

//1. Cycle guard . The protection type is true Then go inside the circulatory body , When false Then skip , Be similar to continue
//2. The following code is equivalent 

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

        4： Cycle step

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

// The output result is 1,3,5,7,9

        5： Nested loop

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

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

// The two are equivalent 

        6： Introduce variables

for (i <-1 to 3;j = 4-i) {
    println("i=" + i + "j=" + j)
}

for (i <- 1 to 3) {
    var j = 4 -i
    println("i=" + i + "j=" + j)
}

// Both equal 

        7： Loop return value

var res = for (i <- 1 to 10) yield {
    i * 2
}
println(res)

// Return the result processed in the traversal result to a new vector Collection , Use yield keyword 
// result  vector（2,4,6,8,10,12,14,16,18,20）

        8： Print in reverse order

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

// Print in reverse order 10 To 1

8、 ... and ：while and do..while Cycle control

        1： And Java The usage is the same

        2：while Cycle control

object TestWhile {
    def main(args: Array[String]): Unit = {
        var i = 0
        while (i < 10) {
            println("i = " + i)
            i += 1
        }
    }
}

        3：do..while control

object TestWhile {
    def main(args: Array[String]): Unit = {
        var i = 0
        do {
            println("i =" + i)
            i += 1
        } while (i < 10）
    }
}

Nine ： Cycle break

        1： Exit the loop in an abnormal way

def main(args: Array[String]): Unit = {
    try {
        for (elem < 1 to 10) {
            println(elem)
            if (elem == 5) throw new RuntimeException
        }
    }catch {
        case e =>
    }

    println(" Normal end of cycle ")
}

        2：Scala Built-in function , Exit loop

import scala.util.control.Breaks

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

        3： Yes break Omit

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 " )
    }
}