Iterative Fibonacci sequence

Question

I implemented a function that prints all the numbers from the Fibonacci sequence until max_num. The minimum value allowed is 0 (so, fib(0) prints 1). It works until 92, and I want to know how to improve the code, in general.

void fib(unsigned int max_num)
{
    unsigned long fib_num = 1;
    unsigned long fib_temp = 0;
    size_t count = 0;

    if (max_num < 0)
    {
        fprintf(stderr, "Please, enter a non-negative number\n");
        return;
    }

    for (; count <= max_num; count++)
    {
        printf("%lu\n", fib_num);
        fib_num += fib_temp;
        fib_temp = fib_num - fib_temp;
    }
}

Answer 1

Consider documenting this function with something like doxygen. At a quick glance, your function can be interpreted two different ways: Print out fib(0), fib(1), ..., or print out all Fibonacci numbers less than or equal to max_num. Documentation will clarify that.

max_num will never be negative. It is defined as an unsigned int, which means it can never hold a negative value. So this:

if (max_num < 0)
{
    fprintf(stderr, "Please, enter a non-negative number\n");
    return;
}

will never happen. (Try calling fib(-2), see what happens)

(Optional) Put size_t count = 0 inside the loop if you can? (You may have to add -std=c99 or something like that to make it work)

for (size_t count = 0; count <= max_num; count++)
{
    printf("%lu\n", fib_num);
    fib_num += fib_temp;
    fib_temp = fib_num - fib_temp;
}