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C Exercises: Find the sum of the even-valued terms from the terms in the Fibonacci sequence

C Programming Practice: Exercise-18 with Solution

In mathematics, the Fibonacci numbers, commonly denoted Fn 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 programming 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

Flowchart:

C Programming Flowchart: Find the sum of the even-valued terms from the terms in the Fibonacci sequence.

C Programming Code Editor:

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What is the difficulty level of this exercise?

C Programming: Tips of the Day

C Programming - Why do all the C files written by my lecturer start with a single # on the first line?

In the very early days of pre-standardised C, if you wanted to invoke the preprocessor, then you had to write a # as the first thing in the first line of a source file. Writing only a # at the top of the file affords flexibility in the placement of the other preprocessor directives.

From an original C draft by the great Dennis Ritchie himself:

12. Compiler control lines

[...] In order to cause [the] preprocessor to be invoked, it is necessary that the very first line of the program begin with #. Since null lines are ignored by the preprocessor, this line need contain no other information.

That document makes for great reading (and allowed me to jump on this question like a mad cat).

I suspect it's the lecturer simply being sentimental - it hasn't been required certainly since ANSI C.

Ref : https://bit.ly/2Mb8OVZ