#define _USE_MATH_DEFINES???

[LN7oGNh0]

Im trying to show pi. I know how to set precision and all that, but I cant seem to get it! I did this:

#define _USE_MATH_DEFINES
#include <cmath> 

Isnt this what I supposed to do? I think there's something to do with M_PI, but I type that in and its still underlined in red in my compiler. What mistake am I making?

EDIT: DO I have to type in all the digits of pi and then define it? just wondering

[Chervil]

I think M_PI may be non-standard, depending on which compiler is used.

You could do this:

#include <iostream>
#include <iomanip>
#include <cmath>

    using namespace std;

int main()
{
    const double PI = 4.0 * atan(1.0);

    cout << "PI = " << setprecision(16) << PI << endl;

    return 0;
}

Output:

PI = 3.141592653589793

Line 9 uses the fact that the angle whose tangent equals 1, is PI/4 radians or 45 degrees. So calculate it once at the start of the program and from then on use the stored value.

[LN7oGNh0]

Ok thank you.