C/math.h/copysign

    
//Declaration: float copysignf(float val, float signval); 
               double copysign(double val, double signval); 
               long double copysignl(long double val, long double signval);  
  #include <math.h>
  #include <stdio.h>
  int main(void)
  {
    printf("%f", copysignf(1.0, -2.0));
   
  }
         
/*
-1.000000*/