# How do I make a sine wave without using an infinitely-increasing time value as input?

I have a basic understanding of sine wave generation. The problem I am facing is that as the input parameter for time gets larger, my sine wave falls apart and starts to look really ugly.

I'd like to calculate a sine wave without depending on an ever increasing time value. How can I do this?

You could restart your time value every 2pi:

if(time > 2*pi)
time -= 2*pi;


If is still okay to increase your time variable infinitely but the input for the sine is to large, just use fmod(time, 2*pi).

• thank you, using fmod worked. It seemed to keep the values between 2*pi. Quick question, what does fmod do? I read this: tutorialspoint.com/c_standard_library/c_function_fmod.htm it says fmod returns the remainder but I don't get why it works. – tmp Sep 5 '15 at 17:27
• basically it returns r in the equation x = n*y + r where x and y are the inputs and n is an integer. – ratchet freak Sep 5 '15 at 18:25
• The reason you hit the issue you did is that as floating point numbers get larger, they lose accuracy. For instance if you start at zero and add one to a floating point number in an infinite loop, there will come a point where adding the 1 results in the same value (ie will have no effect) – Alan Wolfe Sep 6 '15 at 0:52
• @ratchetfreak so is fmod like the modulus operation? – tmp Sep 6 '15 at 15:23