# Kotlin Tail-Recursive Function: Sum of numbers from 1 to n

## Kotlin Function: Exercise-15 with Solution

Write a Kotlin tail-recursive function to calculate the sum of all numbers from 1 to n.

**Sample Solution:**

**Kotlin Code:**

```
tailrec fun sumNumbers(n: Int, currentSum: Int = 0): Int {
if (n == 0) {
return currentSum
}
return sumNumbers(n - 1, currentSum + n)
}
fun main() {
val n = 7
val sum = sumNumbers(n)
println("Sum of numbers from 1 to $n: $sum")
}
```

Sample Output:

Sum of numbers from 1 to 7: 28

**Explanation:**

In the above exercise -

- The "sumNumbers()" function takes two parameters: n, which represents the number up to which we want to calculate the sum, and currentSum, which keeps track of the running sum.
- In the base case, if n becomes 0, it means we have reached the end and return the current sum.
- In each recursive call, we decrement n by 1 and add it to the current sum (currentSum + n).
- 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 sum is computed.

**Kotlin Editor: **

**Previous:** Calculate factorial.

**Next:** Calculate the nth Fibonacci.

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