C Exercises: Sum even-valued in a Fibonacci sequence

Last update on December 20 2024 13:20:02 (UTC/GMT +8 hours)

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:

10

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