CODEWITHSUNDEEP
c++geometryshapes
user3476655
user3476655

Reputation: 11

What's wrong with my C++ code?

I'm trying to create an equilateral triangle that outputs to the console but my code seems to output the triangle at point 0,0.

How can I fix this?

this is what I have:

Header file:

#include "shape.h"
#include "vertex.h"
#include <list>

// An equilateral triangle
class Triangle : public Shape
{ 
    // the radius provides the length of a side
    // and enables a vertex to be plotted from
    // which the other two vertices can be derived
    // via rotation
    int radius;
public:
    // constructor
    Triangle(Vertex point, int radius = 10);

    // calculates and returns a triangle's area
    int area();

    // calculates and returns a triangle's perimeter
    int perimeter();
};

and the cpp file

#include "triangle.h"
#include "vertex.h"
#include <list>

Triangle::Triangle(Vertex point, int radius) : Shape(point)
{
    this->radius = radius;

    this->centroid = Vertex(0,0); 
    vertices.push_back(Vertex(centroid.getY() + radius));
    vertices.push_back(Vertex(centroid.getY() + (radius*2)));
    vertices.push_back(Vertex(centroid.getX() * cos(120) - centroid.getY() * sin(120),centroid.getY() * cos(120) + centroid.getX() * sin(120)));
    vertices.push_back(Vertex(centroid.getX() * cos(240) - centroid.getY() * sin(240),centroid.getY() * cos(240) + centroid.getX() * sin(240)));

    this->centroid = point;
}

// returns the area of an equilateral triangle
int Triangle::area()
{
    return radius*radius*(sqrt(3)/4);
}

// returns the perimeter of an equilateral triangle
int Triangle::perimeter()
{
    return radius *3;
}

I'm not sure what's wrong with it. I have tried many different ways to fix it but I have had no luck in doing so. can somebody please help?

Upvotes: 0

Views: 218

Answers (2)

Martin J.
Martin J.

Reputation: 5118

As noted in the other answer, sin and cos take their arguments in radians, not degrees.
Furthermore, your constructor seems strange. Bear in mind that I don't have all the details behind your code (Vertex, Shape, ...), but assuming that vertices needs to contain the three vertices of your triangle and that Vertex has a constructor taking the three coordinates, I'd try something like this:

Triangle::Triangle(Vertex point, int radius) : Shape(point)
{
    this->radius = radius;
    // in any case, you want the traingle to be centered around the point given as input
    this->centroid = point;

// we can just avoid calling trigonometric functions at runtime
// also, the values for these particular angles are well-known, so we don't need to call any actual trigonometric functions
    static const float COS_60 = 0.5f;
    static const float COS_30 = 0.5f * sqrt(3.f);

    // compute the length of the side of the triangle based on its radius
    // for instance, using any of the six right triangles between the center, a vertice and the projection of the center against one of the sides
    const float side = radius * 2.f * COS_30;
    // more basic geometry
    const float bottomHeight = point.getY() - COS_60 * radius;

    // first vertice is right above the center
    this->vertices.push_back(Vertex(point.getX(), point.getY() + radius));
    // second vertice is at the bottom height, and its X position is offset by half the side
    this->vertices.push_back(Vertex(point.getX() + COS_60 * side, bottomHeight));
    // same, but in the other direction
    this->vertices.push_back(Vertex(point.getX() - COS_60 * side, bottomHeight));

}

Upvotes: 0

tenfour
tenfour

Reputation: 36896

sin, cos, etc use radians, not degrees.

Also you set your centroid at a hard-coded 0,0.

Upvotes: 4

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