cppreference.com > Standard C Math > abs
abs
Syntax:
  #include <stdlib.h>
  int abs( int num );

The abs() function returns the absolute value of num. For example:

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