Is there a function such that f(x)= the decimal part of x ( sister function of integer part function). I'm looking for a little formula that would allow me to convert the degree mesure of an angle into its radian mesure. 

In case the degree mesure is greater than 360° the complete 360° turns contained in the angle do not count. 

So the idea is as follows: (1) first dividing the degree mesure by 360, and keeping only the decimal part of the quotient. 

Then, (2) multiplying the decimal part by 360 and (3) multiplying the result by pi/180 in order to get the redian mesure. 

Is there a known function that allows me to keep only the decimal part of a number? 

I mean, sure this function exists, but does it have a name? Is it possible to find it on some calculators?
Yes. The name for such a function is the fractional part function, and the fractional part of $x$ is usually written as $\{ x \}$. So in this case, the formula would be $\{ \frac{\pi x}{180} \}$.
Yes. The name for such a function is the fractional part function, and the fractional part of $x$ is usually written as $\{ x \}$. So in this case, the formula would be $\{ \frac{\pi x}{180} \}$.