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;
}

• Lúcio Cardoso: Thanks a lot for the answer! I heard some people saying I should stick to the c89 mode. In your opinion, which one is the best?
• Dair: It has a lot to do with how much of the market supports the language... It may have been at the time a better idea to use C89 over C99 because very few compilers supported C99. This isn't true anymore. It might even be better to use C11. (Which I believe is -std=c11). A large part is do you need to support C89? C99? If not, I would just do C99, the for-loop syntax for C89 is particularly annoying to me.
• Dair: For reference there are answers here: stackoverflow.com/a/11926008/667648 That coincide with my comment.
• ElleJay: @LúcioCardoso The only more or less relevant compiler not supporting C99 is VS C compiler afaik. But C is mostly broken under Windows, similar to OpenGL. It works, with a few quirks, but it's not for serious development.