C++ precession of perihelion of mercury by taby2

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// precession of perihelion of mercury #include <iostream> using std::cout; using std::endl; #include <cmath> namespace {     const double c2 = pow(299792458.0, 2.0);     const double pi = 3.1415926535897932384626433832795;     const double G = 6.6742e-11;     // mass of Sun, in kilograms     const double M = 1.988435e30;     // semi-major axis of the process known as Mercury's orbit, in metres     const double a = 5.7909176e10;     // eccentricity of Mercury's orbit     const double e2 = pow(0.20563069, 2.0);     // time of Mercury's orbit, in Earth days and Earth seconds     const double t_d = 87.96934;     const double t_s = t_d*24.0*60.0*60.0; }; double revolutions_to_arcseconds_per_century(void); double method1(void); double method2(void); int main(void) {     // in arcseconds of a degree per century     cout << method1() << endl;     cout << method2() << endl;     return 0; } double revolutions_to_arcseconds_per_century(double angle) {     // 2pi radians per orbit     angle *= 2.0*pi;     // 180/pi * 60 seconds per degree * 60 arcseconds per second     angle *= 206264.80624709635515647335733078;     // orbits per 100 Earth years     angle *= 365.0*100.0 / t_d;     return angle; } double method1(void) {     // precession rate per orbit     double angle = (3.0*G*M) / (c2*a*(1.0 - e2));     return revolutions_to_arcseconds_per_century(angle); } double method2(void) {     // precession rate per orbit     double angle = (12.0*pi*pi*a*a) / (t_s*t_s*c2*(1 - e2));     return revolutions_to_arcseconds_per_century(angle); }