corners of a triangle form degrees

[gary24]

the code looks like this
const double PI = 3.1415926535897;

struct mStruct
{
double A_towerx;
double A_towery;
double B_towerx;
double B_towery;
double C_towerx;
double C_towery;
};

void modify(mStruct *v,double build_radius)
{
double x_theta = 210 * PI/180,y_theta = 330 * PI/180,z_theta = 90 * PI/180;

v->A_towerx = build_radius * cos(x_theta);
v->A_towery = build_radius * sin(x_theta);
v->B_towerx = build_radius * cos(y_theta);
v->B_towery = build_radius * sin(y_theta);
v->C_towerx = build_radius * cos(z_theta);
v->C_towery = build_radius * sin(z_theta);

the out put is

A corner x= -86.6025
A corner y= -50
B corner x= 86.6025
B corner y= -50
C corner x= 4.66906e-012
C corner y= 100

the build radius I used was 100

every thing is correct except the C corner x, that should = 0

anyone know where I am going wrong?.

thanks gary

[TheIdeasMan]

every thing is correct except the C corner x, that should = 0

It is zero, just that the representation of double is not exact. If you print the value with std::fixed, and a std::precision less than 12 it will print appropriately.

Some other improvements:

constexpr is stronger than const ; PI / 180.0 is also a constant value:

constexpr double PI = 3.1415926535897; 
constexpr DTR = PI /180.0; // DTR is Degrees To Radians 

Avoid declaring more than 1 variable per line of code, it will save you problems later.

Instead of 6 variables in your struct, consider having a struct Point, then have a std::vector<Point>.

Pass this std::vector to the function by reference, thus avoiding a raw pointer.


In C++, a struct is almost the same as a class - the only difference being the default access is public with struct, and private with class. So alternatively, your struct could be a class with a constructor and an interface of functions.

Edit: This will be better than having your data public.

Good Luck !!

Edit: I have to go out for awhile, I may not be able to reply to any questions.

[dhayden]

In PI, the 14th digit to the right of the decimal point is 9, so if you're going to use 13 digits, then you should round the last one up from 7 to 8.

[gary24]

out put now with added

std::cout.precision(4);
cout <<"A corner x= "<<std::fixed<<towers.A_towerx<<endl;

A corner x= -86.6025
A corner y= -50.0000
B corner x= 86.6025
B corner y= -50.0000
C corner x= 0.0000
C corner y= 100.0000

looks correct not sure how to setup std::vector haven't used yet

Thanks for your help at least I am on the right track and have a working function.

gary