#include <stdlib.h>
  int abs( int num );

   int magic_number = 10;
   cout << "Enter a guess: ";
   cin >> x;
   cout << "Your guess was " << abs( magic_number - x ) << " away from the magic number." << endl;          

  #include <math.h>
  double acos( double arg );

The acos() function returns the arc cosine of arg, which will be in the range [0, pi]. arg should be between -1 and 1. If arg is outside this range, acos() returns NAN and raises a floating-point exception.

  #include <math.h>
  double asin( double arg );

The asin() function returns the arc sine of arg, which will be in the range [-pi/2, +pi/2]. arg should be between -1 and 1. If arg is outside this range, asin() returns NAN and raises a floating-point exception.

  #include <math.h>
  double atan( double arg );

The function atan() returns the arc tangent of arg, which will be in the range [-pi/2, +pi/2].

  #include <math.h>
  double atan2( double y, double x );

The atan2() function computes the arc tangent of y/x, using the signs of the arguments to compute the quadrant of the return value.

Note the order of the arguments passed to this function.

  #include <math.h>
  double ceil( double num );

The ceil() function returns the smallest integer no less than num. For example,

   y = 6.04;
   x = ceil( y );               

would set x to 7.0.

  #include <math.h>
  double cos( double arg );

The cos() function returns the cosine of arg, where arg is expressed in radians. The return value of cos() is in the range [-1,1]. If arg is infinite, cos() will return NAN and raise a floating-point exception.

  #include <math.h>
  double cosh( double arg );

The function cosh() returns the hyperbolic cosine of arg.

  #include <stdlib.h>
  div_t div( int numerator, int denominator );

The function div() returns the quotient and remainder of the operation numerator / denominator. The div_t structure is defined in stdlib.h, and has at least:

   int quot;   // The quotient
   int rem;    // The remainder         

For example, the following code displays the quotient and remainder of x/y:

   div_t temp;
   temp = div( x, y );
   printf( "%d divided by %d yields %d with a remainder of %d\n",
           x, y, temp.quot, temp.rem );         

  #include <math.h>
  double exp( double arg );

The exp() function returns e (2.7182818) raised to the argth power.

  #include <math.h>
  double fabs( double arg );

The function fabs() returns the absolute value of arg.

  #include <math.h>
  double floor( double arg );

The function floor() returns the largest integer not greater than arg. For example,

   y = 6.04;
   x = floor( y );              

would result in x being set to 6.0.

  #include <math.h>
  double fmod( double x, double y );

The fmod() function returns the remainder of x/y.

  #include <math.h>
  double frexp( double num, int* exp );

The function frexp() is used to decompose num into two parts: a mantissa between 0.5 and 1 (returned by the function) and an exponent returned as exp. Scientific notation works like this:

   num = mantissa * (2 ^ exp)           

  #include <stdlib.h>
  long labs( long num );

The function labs() returns the absolute value of num.

  #include <math.h>
  double ldexp( double num, int exp );

The ldexp() function returns num * (2 ^ exp). And get this: if an overflow occurs, HUGE_VAL is returned.

  #include <stdlib.h>
  ldiv_t ldiv( long numerator, long denominator );

Testing: adiv_t, div_t, ldiv_t.

The ldiv() function returns the quotient and remainder of the operation numerator / denominator. The ldiv_t structure is defined in stdlib.h and has at least:

   long quot;  // the quotient
   long rem;   // the remainder         

  #include <math.h>
  double log( double num );

The function log() returns the natural (base e) logarithm of num. There's a domain error if num is negative, a range error if num is zero.

In order to calculate the logarithm of x to an arbitrary base b, you can use:

  double answer = log(x) / log(b);

  #include <math.h>
  double log10( double num );

The log10() function returns the base 10 (or common) logarithm for num. There's a domain error if num is negative, a range error if num is zero.

  #include <math.h>
  double modf( double num, double *i );

The function modf() splits num into its integer and fraction parts. It returns the fractional part and loads the integer part into i.

  #include <math.h>
  double pow( double base, double exp );

The pow() function returns base raised to the expth power. There's a domain error if base is zero and exp is less than or equal to zero. There's also a domain error if base is negative and exp is not an integer. There's a range error if an overflow occurs.

  #include <math.h>
  double sin( double arg );

The function sin() returns the sine of arg, where arg is given in radians. The return value of sin() will be in the range [-1,1]. If arg is infinite, sin() will return NAN and raise a floating-point exception.

  #include <math.h>
  double sinh( double arg );

The function sinh() returns the hyperbolic sine of arg.

  #include <math.h>
  double sqrt( double num );

The sqrt() function returns the square root of num. If num is negative, a domain error occurs.

  #include <math.h>
  double tan( double arg );

The tan() function returns the tangent of arg, where arg is given in radians. If arg is infinite, tan() will return NAN and raise a floating-point exception.

  #include <math.h>
  double tanh( double arg );

The function tanh() returns the hyperbolic tangent of arg.