Kotlin-基础语法练习一

Example:

fun main(args: Array<String>) {
    var a= 10 + 20
    println(a)
}

Output:

30

Arithmetic Operators-算术运算符:

Operators	Meaning	Expression	Translate to
+	Addition	a + b	a.plus(b)
-	Subtraction	a - b	a.minus(b)
*	Multiplication	a * b	a.times(b)
/	Division	a / b	a.div(b)
%	Modulus	a % b	a.rem(b)

Example:

fun main(args: Array<String>)
{
    var a = 20 
    var b = 4 
    println("a + b = " + (a + b))
    println("a - b = " + (a - b))
    println("a * b = " + (a.times(b)))
    println("a / b = " + (a / b))
    println("a % b = " + (a.rem(b)))
}

Output:

a + b = 24
a - b = 16
a * b = 80
a / b = 5
a % b = 0

Relational Operators-关系运算符

Operators	Meaning	Expression	Translate to
>	greater than	a > b	a.compareTo(b) > 0
<	less than	a < b	a.compareTo(b) < 0
>=	greater than or equal to	a >= b	a.compareTo(b) >= 0
<=	less than or equal to	a <= b	a.compareTo(b) <= 0
==	is equal to	a == b	a?.equals(b) ?: (b === null)
!=	not equal to	a != b	!(a?.equals(b) ?: (b === null)) > 0

Example:

fun main(args: Array<String>)
{
    var c = 30
    var d = 40
    println("c > d = "+(c>d))
    println("c < d = "+(c.compareTo(d) < 0))
    println("c >= d = "+(c>=d))
    println("c <= d = "+(c.compareTo(d) <= 0))
    println("c == d = "+(c==d))
    println("c != d = "+(!(c?.equals(d) ?: (d === null))))
}

Output:

c > d = false
c < d = true
c >= d = false
c <= d = true
c == d = false
c != d = true

Assignment Operators-赋值运算符

Operators	Expression	Translate to
=	a = 5	a.equalto(5)
+=	a = a + b	a.plusAssign(b) > 0
-=	a = a - b	a.minusAssign(b) < 0
*=	a = a * b	a.timesAssign(b)>= 0
/=	a = a / b	a.divAssign(b) <= 0
%=	a = a % b	a.remAssign(b)

Example:

fun main(args : Array<String>){
 var a = 10
    var b = 5
    a+=b
    println(a)
    a-=b
    println(a)
    a*=b
    println(a)
    a/=b
    println(a)
    a%=b
    println(a)

}

Output:

15
10
50
10
0

Unary Operators-单目运算符

Operators	Expression	Translate to
++	++a or a++	a.inc()
--	--a or a--	a.dec()

Example:

fun main(args : Array<String>){
    var e=10
    var flag = true
    println("First print then increment: "+ e++)
    println("First increment then print: "+ ++e)
    println("First print then decrement: "+ e--)
    println("First decrement then print: "+ --e)
}

Output:

First print then increment: 10
First increment then print: 12
First print then decrement: 12
First decrement then print: 10

Logical Operatorsz-逻辑运算符

Operators	Meaning	Expression
&&	Return true if all expressions are true	(a>b) && (a>c)
||	Return true if any of the expressions is true	(a>b)
!	Return the complement of the expression	a.not()

Example:

fun main(args : Array<String>){
    var x = 100
    var y = 25
    var z = 10
    var result = false
    if(x > y && x > z)
     println(x)
    if(x < y || x > z)
     println(y)
    if( result.not())
     println("Logical operators")
}

Output:

100
25
Logical operators

Bitwise Operators-位运算符

Operators	Meaning	Expression
shl	signed shift left	a.shl(b)
shr	signed shift right	a.shr(b)
ushr	unsigned shift right	a.ushr()
and	bitwise and	a.and(b)
or	bitwise or	a.or()
xor	bitwise xor	a.xor()
inv	bitwise inverse	a.inv()

Example:

fun main(args: Array<String>)
{
    println("5 signed shift left by 1 bit: " + 5.shl(1))
    println("10 signed shift right by 2 bits: : " + 10.shr(2))
    println("12 unsigned shift right by 2 bits:  " + 12.ushr(2))
    println("36 bitwise and 22: " + 36.and(22))
    println("36 bitwise or 22: " + 36.or(22))
    println("36 bitwise xor 22: " + 36.xor(22))
    println("14 bitwise inverse is: " + 14.inv())
}

Output:

5 signed shift left by 1 bit: 10
10 signed shift right by 2 bits: : 2
12 unsigned shift right by 2 bits:  3
36 bitwise and 22: 4
36 bitwise or 22: 54
36 bitwise xor 22: 50
14 bitwise inverse is: -15

Kotlin Output-Kotlin 输出

print() function // prints text

println() function // prints text and then moves the cursor to a new line

Example:

fun main(args: Array<String>)
{
    print("Hello, Geeks! ")
    println("This is Kotlin tutorial.")
    print("By GFG!")
}

Output:

Hello, Geeks! This is Kotlin tutorial.
By GFG!

Print Literals and Variables-打印字面量和变量

Example:

fun sum(a: Int,b: Int) : Int{
    return a + b
}

fun main(args: Array<String>){

    var a = 10
    var b = 20
    var c = 30L
    var marks = 40.4

    println("Sum of {$a} and {$b} is : ${sum(a,b)}")
    println("Long value is: $c")
    println("marks")
    println("$marks")
}

Output:

Sum of {10} and {20} is : 30
Long value is: 30
marks
40.4 

Kotlin Input-Kotlin 输入

readline() method

Scanner class

Example:

fun main(args : Array<String>) {
    print("Enter text: ")
    var input = readLine()
    print("You entered: $input")
}

Output:

Enter text: Hello, Geeks! You are learning how to take input using readline()
You entered: Hello, Geeks! You are learning how to take input using readline()

使用Scanner类从用户获取输入

Example:

import java.util.Scanner

fun main(args: Array<String>) {
    
    // create an object for scanner class
    val number1 = Scanner(System.`in`)       
    print("Enter an integer: ")
    // nextInt() method is used to take 
    // next integer value and store in enteredNumber1 variable
    var enteredNumber1:Int = number1.nextInt()
    println("You entered: $enteredNumber1")

    val number2 = Scanner(System.`in`)
    print("Enter a float value: ")

    // nextFloat() method is used to take next
    // Float value and store in enteredNumber2 variable
    var enteredNumber2:Float = number2.nextFloat()
    println("You entered: $enteredNumber2")

    val booleanValue = Scanner(System.`in`)
    print("Enter a boolean: ")
    // nextBoolean() method is used to take 
    // next boolean value and store in enteredBoolean variable
    var enteredBoolean:Boolean = booleanValue.nextBoolean()
    println("You entered: $enteredBoolean")
}

Output:

Enter an integer: 123
You entered: 123
Enter a float value:  40.45
You entered: 40.45
Enter a boolean:  true
You entered: true

在不使用Scanner类的情况下从用户获取输入：

readline () ! !将输入作为字符串，并在后面加上（!!）以确保输入值不为空。
Example:

fun main(args: Array<String>) {

    print("Enter an Integer value: ")
    val string1 = readLine()!!  

    // .toInt() function converts the string into Integer
    var integerValue: Int = string1.toInt() 
    println("You entered: $integerValue")

    print("Enter a double value: ")
    val string2= readLine()!!

    // .toDouble() function converts the string into Double
    var doubleValue: Double = string2.toDouble() 
    println("You entered: $doubleValue")
}

Output:

Enter an Integer value: 123
You entered: 123
Enter a double value:  22.22222
You entered: 22.22222

Kotlin Type Conversion- Kotlin类型转换

类型转换（也称为类型强制转换）是指将一种数据类型变量的实体更改为另一种数据类型。正如我们所知，Java支持从较小数据类型到较大数据类型的隐式类型转换。整数值可以分配给long数据类型。
但是，Kotlin不支持隐式类型转换。整数值不能分配给长数据类型。
Example:

public class TypecastingExample {  
   public static void main(String args[]) {  
      byte p = 12;  
      System.out.println("byte value : "+p);
      
      // Implicit Typecasting 
      // integer value can be assigned
      // to long data type
      long q = p;
    }
 }

Output:

var myNumber = 100
var myLongNumber: Long = myNumber       // Compiler error
// Initializer type mismatch: expected 'Long', actual 'Int'.

var myNumber = 100
var myLongNumber: Long = myNumber.toLong()     // compiles successfully

下面的辅助函数可用于将一种数据类型转换为另一种数据类型：

toByte() 
toShort() 
toInt() 
toLong() 
toFloat() 
toDouble() 
toChar() 

Example:

fun main(args: Array<String>)
{
  
    println("259 to byte: " + (259.toByte()))
    println("50000 to short: " + (50000.toShort()))
    println("21474847499 to Int: " + (21474847499.toInt()))
    println("10L to Int: " + (10L.toInt()))
    println("22.54 to Int: " + (22.54.toInt()))
    println("22 to float: " + (22.toFloat()))
    println("65 to char: " + (65.toChar()))
    // Char to Number is deprecated in kotlin
    println("A to Int: " + ('A'.toInt()))
}

Output:

259 to byte: 3
50000 to short: -15536
21474847499 to Int: 11019
10L to Int: 10
22.54 to Int: 22
22 to float: 22.0
65 to char: A
A to Int: 65