Compare double base on precision : double « Data Types « C++ Tutorial

1. C++ Tutorial
2. Data Types
3. double

#include <iostream>
#include <cmath>

using namespace std;

bool doubleEquals(double left, double right, double epsilon) {
  return (fabs(left - right) < epsilon);
}

bool doubleLess(double left, double right, double epsilon, bool orequal = false) {
  if (fabs(left - right) < epsilon) {
    return (orequal);
  }
  return (left < right);
}

bool doubleGreater(double left, double right, double epsilon, bool orequal = false) {
  if (fabs(left - right) < epsilon) {
    return (orequal);
  }
  return (left > right);
}

int main( ) {
  double first = 0.33333333;
  double second = 1.0 / 3.0;

  cout << first << endl;
  cout << second << endl;

  cout << boolalpha << (first == second) << endl;
  cout << doubleEquals(first, second, .0001) << endl;
  cout << doubleLess(first, second, .0001) << endl;
  cout << doubleGreater(first, second, .0001) << endl;
  cout << doubleLess(first, second, .0001, true) << endl;
  cout << doubleGreater(first, second, .0001, true) << endl;
}

0.333333
0.333333
false
true
false
false
true
true