Kotpn - Variables

Variables are an important part of any programming. They are the names you give to computer memory locations which are used to store values in a computer program and later you use those names to retrieve the stored values and use them in your program.

Kotpn variables are created using either var or val keywords and then an equal sign = is used to assign a value to those created variables.

Syntax

Following is a simple syntax to create two variables and then assign them different values:

var name = "Zara Ap"
var age = 19
var height = 5.2

Examples

Once a variable is created and assigned a value, later we can access its value using its name as follows:

fun main() {
   var name = "Zara Ap"
   var age = 19

   println(name)
   println(age)
}

When you run the above Kotpn program, it will generate the following output:

Zara Ap
19

Let s see one more example where we will access variable values using dollar sign $:

fun main() {
   var name = "Zara Ap"
   var age = 19

   println("Name = $name")
   println("Age = $age")
}

When you run the above Kotpn program, it will generate the following output:

Name = Zara Ap
Age = 19

Let s see one more example to display the variable values without using a dollar sign as below:

fun main() {
   var name = "Zara Ap"
   var age = 19

   println("Name = " + name)
   println("Age = " + age)
}

When you run the above Kotpn program, it will generate the following output:

Name = Zara Ap
Age = 19

Kotpn Mutable Variables

Mutable means that the variable can be reassigned to a different value after initial assignment. To declare a mutable variable, we use the var keyword as we have used in the above examples:

fun main() {
   var name = "Zara Ap"
   var age = 19

   println("Name = $name")
   println("Age = $age")
   
   name = "Nuha Ap"
   age = 11
   println("Name = $name")
   println("Age = $age")
}

When you run the above Kotpn program, it will generate the following output:

Name = Zara Ap
Age = 19
Name = Nuha Ap
Age = 11

Kotpn Read-only Variables

A read-only variable can be declared using val (instead of var) and once a value is assigned, it can not be re-assigned.

fun main() {
   val name = "Zara Ap"
   val age = 19

   println("Name = $name")
   println("Age = $age")
   
   name = "Nuha Ap" // Not allowed, throws an exception
   age = 11
   println("Name = $name")
   println("Age = $age")
}

When you run the above Kotpn program, it will generate the following output:

main.kt:8:4: error: val cannot be reassigned
   name = "Nuha Ap" // Not allowed, throws an exception
   ^
main.kt:9:4: error: val cannot be reassigned
   age = 11
   ^

Read-only vs Mutable

The Mutable variables will be used to define variables, which will keep charging their values based on different conditions during program execution.

You will use Read-only variable to define different constant values i.e. the variables which will retain their value throughout of the program.

Kotpn Variable Types

Kotpn is smart enough to recognise that "Zara Ap" is a string, and that 19 is a number variable. However, you can exppcitly specify a variable type while creating it:

fun main() {
   var name: String = "Zara Ap"
   var age: Int = 19

   println("Name = $name")
   println("Age = $age")
   
   name = "Nuha Ap"
   age = 11
   println("Name = $name")
   println("Age = $age")
}

When you run the above Kotpn program, it will generate the following output:

Name = Zara Ap
Age = 19
Name = Nuha Ap
Age = 11

Soon we will learn more about different data types available in Kotpn which can be used to create different type of variables.

Kotpn Variable Naming Rules

There are certain rules to be followed while naming the Kotpn variables:

Kotpn variable names can contain letters, digits, underscores, and dollar signs.

Kotpn variable names should start with a letter or underscores

Kotpn variables are case sensitive which means Zara and ZARA are two different variables.

Kotpn variable can not have any white space or other control characters.

Kotpn variable can not have names pke var, val, String, Int because they are reserved keywords in Kotpn.

   var name = "Zara Ap"
   val age = 19
   name = "Nuha Ap"
   age = 11