Create FindAverageOfNumbersByRecursion.dart (#5604)

Co-authored-by: Harsh Raj <harshraj8843@gmail.com>

program/program/find-average-of-numbers-by-recursion/FindAverageOfNumbersByRecursion.dart

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+import 'dart:io';
+
+double findAverage(List<int> numbers, int index, double sum) {
+  // Base case: when index reaches the end of the list
+  if (index == numbers.length) {
+    // Return the average
+    return sum / numbers.length;
+  } else {
+    // Recursive case: add current number to sum and move to the next index
+    return findAverage(numbers, index + 1, sum + numbers[index]);
+  }
+}
+
+void main() {
+  print("Enter the numbers separated by space:");
+  String input = stdin.readLineSync()!;
+  List<String> numberStrings = input.split(' ');
+
+  // Convert input strings to integers
+  List<int> numbers = numberStrings.map(int.parse).toList();
+
+  // Calculate the average using recursion
+  double average = findAverage(numbers, 0, 0);
+
+  print("Average of the numbers: $average");
+}