Kotlin - Basic Syntax

An entry point of a Kotlin application is the main() function. A function can be defined as a block of code designed to perform a particular task.
Let's start with a basic Kotlin program to print "Hello, World!" on the standard output:
fun main() {
   var string: String  = "Hello, World!"
   println("$string")
}

When you run the above Kotlin program, it will generate the following output:
Hello, World!

Another form of main() function accepts a variable number of String arguments as follows:
fun main(args: Array<String>){
    println("Hello, world!")
}

When you run the above Kotlin program, it will generate the following output:
Hello, World!

If you have observed, its clear that both the programs generate same output, so it is very much optional to pass a parameter in main() function starting from Kotlin version 1.3.
The print() is a function in Kotlin which prints its argument to the standard output, similar way the println() is another function which prints its argument on the standard output but it also adds a line break in the output.
Let's try the following program to understand the difference between these two important functions:
fun main(args: Array<String>){
    println("Hello,")
    println(" world!")

    print("Hello,")
    print(" world!")
}

When you run the above Kotlin program, it will generate the following output:
Hello, 
 world!
Hello, world!

Both the functions (print() and println()) can be used to print numbers as well as strings and at the same time to perform any mathematical calculations as below:
fun main(args: Array<String>){
    println( 200 )
    println( "200" )
    println( 2 + 2 )

    print(4*3)
}

When you run the above Kotlin program, it will generate the following output:
200
200
4
12

Kotlin code statements do not require a semicolon (;) to end the statement like many other programming languages, such as Java, C++, C#, etc. do need it.
Though you can compile and run a Kotlin program with and without semicolon successfully as follows:
fun main() {
    println("I'm without semi-colon")
    
    println("I'm with semi-colon");
}

When you run the above Kotlin program, it will generate the following output:
I'm without semi-colon
I'm with semi-colon

So as a good programming practice, it is not recommended to add a semicolon in the end of a Kotlin statement.
Kotlin code is usually defined in packages though package specification is optional. If you don't specify a package in a source file, its content goes to the default package.
If we specify a package in Kotlin program then it is specified at the top of the file as follows:
package org.tutorialspoint.com

fun main() {
    println("Hello, World!")
}

When you run the above Kotlin program, it will generate the following output:
Hello, World!

Q 1 - Kotlin main() function should have a mandatory parameter to compile the code successfully:
A - True 
B - False
No it is not mandatory that Kotlin main() function should always have a parameter. If you need to pass multiple arguments through an array of string then you can use the paremeter like main(args: Array<String>), otherwise it is not required.
Q 2 - What will be the output of the following Kotlin program
fun main() {
    println("1"); println("2")
}

A - This will give a syntax error
B - It will print 12
C - 1 followed by 2 in the next line
D - None of the above
Though Kotlin does not recommend using a semicolon in the end of the statement, still if you want to separate two statements in a single line then you can separate them using a semicolon otherwise you will get compile time error.
Q 3 - Which of the following statement is correct in Kotlin
A - A Kotlin program must have a main() function
B - A Kotlin program can be compiled without a main() function
C - It is mandatory to have a print() or println() functions in a Kotlin program
D - All statements are correct from Kotlin programming point of view
Only A statement is correct here, because we can not run a Kotlin program without main() function, which is called an entry point for Kotlin program. It does not matter if you use print() or println() functions within a Kotlin program.

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