Declaring variables

To declare a variable in Kotlin, we use either the val or var keywords.

Let's take a look at the following example:

val number = 10
println(number)

The preceding code prints the value that is assigned to a variable number, as can be seen in the following screenshot:

However, if we try to change the value assigned to the number, we will get a compilation error. Take a look at the following code:

val number = 10
println(number)
number = 11
println(number)

The output is as follows:

This is because val is immutable in Kotlin. This means that once a value is assigned, it cannot be modified. The keyword var, however, can be used to create a mutable variable.

Now consider the code for 3_valnVar.kts:

val number = 10
println(number)

var anotherNumber = 15
println(anotherNumber)

anotherNumber = 20
println(anotherNumber)

The output for the preceding code is as follows:

Let's examine what happens if we assign a string value to the preceding code:

val number = 10
println(number)

var anotherNumber = 15
println(anotherNumber)

anotherNumber = "20"
println(anotherNumber)

Compile this and see what happens:

In this case, the compiler throws an error saying that the type is mismatched. This is because the anotherNumber variable was inferred to be of type int and, as a result, we cannot assign a different type.

The type is inferred from the context and type safety is also guaranteed.