Get absolute value in C++
Get absolute value of argument.
Include <csdlib> and use abs() for integer, include <cmath> and use abs() or fabs() for decimal.
get_absolute_value.cpp 
#include <iostream>
#include <cstdlib>  // abs() for integer
#include <cmath>    // abs() for float, and fabs()

int main() {
  // Get absolute value of integer
  std::cout << "Absolute value of  5 is " << std::abs(5) << std::endl;
  std::cout << "Absolute value of -5 is " << std::abs(-5) << std::endl;

  // Get absolute value of float
  std::cout << "Absolute value of  5.5 is " << std::abs(5.5) << std::endl;
  std::cout << "Absolute value of -5.5 is " << std::abs(-5.5) << std::endl;

  // Get absolute value of float 2
  std::cout << "Absolute value of  5.5 is " << std::fabs(5.5) << std::endl;
  std::cout << "Absolute value of -5.5 is " << std::fabs(-5.5) << std::endl;
  return 0;
}
Result 
$ g++ get_absolute_value.cpp -o get_absolute_value
$ ./get_absolute_value
Absolute value of  5 is 5
Absolute value of -5 is 5
Absolute value of  5.5 is 5.5
Absolute value of -5.5 is 5.5
Absolute value of  5.5 is 5.5
Absolute value of -5.5 is 5.5