# Kotlin Tail-Recursive function: Calculate the nth Fibonacci

## Kotlin Function: Exercise-16 with Solution

Write a Kotlin tail-recursive function to calculate the nth Fibonacci number.

**Sample Solution:**

**Kotlin Code:**

```
tailrec fun fibonacci(n: Int, a: Long = 0, b: Long = 1): Long {
if (n == 0) {
return a
}
return fibonacci(n - 1, b, a + b)
}
fun main() {
val n = 9
val fibonacciNumber = fibonacci(n)
println("The $n-th Fibonacci number is: $fibonacciNumber")
}
```

Sample Output:

The 9-th Fibonacci number is: 34

**Explanation:**

In the above exercise -

- The "fibonacci()" function takes three parameters: n, which represents the position of the Fibonacci number to be calculated, a and b which are used to keep track of the previous two Fibonacci numbers.
- In the base case, if n becomes 0, it means we have reached the desired position and return the current Fibonacci number a.
- In each recursive call, we decrement n by 1 and calculate the next Fibonacci number by adding the previous two Fibonacci numbers (a + b). The current value of b becomes the new value of a, and the sum a + b becomes the new value of b.
- We use tail recursion by making the recursive call directly without additional computation.
- The recursive calls continue until the base case is reached and the final Fibonacci number is computed.

**Kotlin Editor: **

**Previous:** Sum of numbers from 1 to n.

**Next:** Calculate the power of a number.

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