fmod
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  
<math.h>
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|   float       fmodf( float x, float y ); 
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(since C99) | |
|   double      fmod( double x, double y ); 
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|   long double fmodl( long double x, long double y ); 
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(since C99) | |
Computes the remainder of the division operation x/y.
[edit] Parameters
| x, y | - | floating point values | 
[edit] Return value
Remainder of dividing arguments. The result has the same sign as x.
[edit] See also
|    (C99)  | 
   the quotient and remainder of integer division  (function)  | 
|    (C99) 
 | 
   signed remainder of the division operation   (function)  |