C Exercises: Sum even-valued in a Fibonacci sequence

Last update on August 09 2025 12:47:43 (UTC/GMT +8 hours)

18. Sum of Even-Valued Fibonacci Terms Variants

In mathematics, the Fibonacci numbers, commonly denoted F_n form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is, and for n > 1. By starting with 1 and 2, the first 10 terms will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, . . .
Write a C program to find the sum of the even-valued terms from the terms in the Fibonacci sequence whose values do not exceed one million.

C Code:

#include <stdio.h>
int main(void)
{
  unsigned int x1 = 1, x2 = 1, x3 = 2, num_sum = 0;
  while (x3 < 10) {
    x3 = x1 + x2;
    num_sum += x3 * !(x3%2);
    x1 = x2;
    x2 = x3;
  }
  printf("%u\n", num_sum);
  return 0;
}

Sample Output:

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to find the sum of even Fibonacci numbers not exceeding one million using an iterative approach.
Write a C program to generate Fibonacci numbers and sum only the even-valued ones with a for loop.
Write a C program to compute the sum of even Fibonacci terms recursively.
Write a C program to generate Fibonacci numbers, filter even ones, and then calculate their total using a while loop.

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