What is the difference between var and val in Kotlin?

The main difference between var and val in Kotlin is that var declares a mutable variable whose value can be changed, while val declares an immutable variable whose value cannot be changed after it is assigned[1][2][4].

Some key points:

• var variables can be reassigned to a new value at any point in the code[1][2]. For example:

var x = 5
x = 10 // OK

• val variables are read-only and cannot be reassigned[1][2][4]. Attempting to reassign a val will result in a compile error. For example:

val y = 5 
y = 10 // Error: Val cannot be reassigned

• However, the properties of an object assigned to a val can still be changed[1][2]. For example:

val book = Book("Java", 1000)
book.name = "Kotlin" // OK, property can be changed

• val is similar to the final keyword in Java, making the variable immutable[4].

• var is useful when you need to...