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How to print even Fibonacci numbers

Educative Answers Team

The Fibonacci sequence can be implemented using recursion. An illustration of a recursion tree is shown below:

%0 node_1 fib(5) node_2 fib(4) node_1->node_2 node_3 fib(3) node_1->node_3 node_1577726604844 fib(3) node_2->node_1577726604844 node_1577726620200 fib(2) node_2->node_1577726620200 node_1577726702498 fib(2) node_1577726604844->node_1577726702498 node_1577726732636 fib(1) node_1577726604844->node_1577726732636 node_1577726761027 fib(1) node_1577726702498->node_1577726761027 node_1577726713501 fib(0) node_1577726702498->node_1577726713501 node_1577726692584 fib(1) node_1577726620200->node_1577726692584 node_1577726683361 fib(0) node_1577726620200->node_1577726683361 node_1577726698379 fib(2) node_3->node_1577726698379 node_1577726705115 fib(1) node_3->node_1577726705115 node_1577726765267 fib(1) node_1577726698379->node_1577726765267 node_1577726739678 fib(0) node_1577726698379->node_1577726739678
Recursion tree for the 5th term of Fibonacci sequence

An additional check for an even number can be combined with the same algorithm to print only even Fibonacci numbers.


#include <iostream>
using namespace std;

// Recursive algorithm:
int evenFibonacci(int n){
  if(n == 0 || n == 1)
    return n;

  return evenFibonacci(n - 1) + evenFibonacci(n - 2);

int main() {
  // The number of even Fibonacci numbers to print:
  int n = 5;

  int x;
  for(int i = 0; n > 0; i++){
    x = evenFibonacci(i);
    // Check if the number returned is even:
    if(x % 2 == 0){
      cout << x << " ";
  return 0;


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