Area of polygons (Hint Appreciated)

[remedys]

Hello, my name is Trevor and this is my first post! I was wondering if someone could give me a hint on an assignment I was given to calculate the area of regular polygons. I know there might have been an easier way to do this but I thought what I have done so far to be okay. However, the pentagon and heptagon values always come out wrong for some reason. Specifically, the pentagon spits out a value of 0 while heptagon is just wrong in general. The long decimals inside their formulas was from constants in their formulas which involved COT and TAN values.

#include <iostream>
#include <stdio.h>
#include <math.h>
#include <string>
using namespace std;
int main ()
{
    float A;
    float total;
    float n;
    cout <<"Please enter the number of sides for the figure between 3-8       ";
    cin >> n;
    if (n<3)
    {
        cout<<"Please enter a valid digit.";
    }
    if (n>8)
    {
        cout<<"Please enter a valid digit.";
    }
    if (n==3)
    {
    cout <<"The figure you have chosen is equilateral triangle.     ";
        cout <<"The area formula is: ((sqrt(3))/4)*(A^2)   Please enter side length A      ";
        cin >> A;
        float total=((sqrt(3))/4)*(A*A);
        cout<<total;
    }
        if (n==4)
    {
    cout <<"The figure you have chosen is square.     ";
        cout <<"The area formula is: A^2.  Please enter side length A      ";
        cin >> A;
        float total=(A*A);
        cout<<total;
    }
        if (n==5)
    {
    cout <<"The figure you have chosen is pentagon.     ";
        cout <<"The area formula is: (1/4)*(sqrt(5(5+2sqrt(5))))*A^2 Please enter side length A      ";
        cin >> A;
        float total=((1/2)*((A/2)/.726542528)*(A*5));
        cout<<total;
   }
        if (n==6)
    {
        cout <<"The figure you have chosen is hexagon.     " ;
        cout <<"The area formula is: ((3*sqrt(3))/2)*(A^2)  Please enter side length A      ";
        cin >> A;
        float total=((3*sqrt(3))/2)*(A*A);
        cout<<total;
    }
        if (n==7)
    {
    cout <<"The figure you have chosen is heptagon.     ";
        cout <<"The area formula is: (7/4)*(A^2)*cot(180/7)   Please enter side length A      ";
        cin >> A;
        float total=((2.0765213965692558)*(A*A)*(7/4));
        cout<<total;
    }
        if (n==8)
    {
    cout <<"The figure you have chosen is octagon.     ";
        cout <<"The area formula is: 2*(1+sqrt(2))*(A^2)  Please enter side length A      ";
        cin >> A;
        float total=2*(1+(sqrt(2)))*(A*A);
        cout<<total;
    }
    }

[keskiverto]

#include <iostream>

int main() {
  std::cout << "Integer division " << ( 7 / 4 ) << '\n';
  std::cout << "Floating point division " << ( 7 / 4.0 ) << '\n';

  return 0;
}

Does the output of this demonstrate the problem?

[dhayden]

More specifically, at line 42, 1/2 uses integer division so the result is always zero. At line 58, 7/4 uses integer division and the result is always 1.

[TheIdeasMan]

Hi remedys ,

Just wondering, can you figure out how to use the same formula for all the shapes? Not sure whether that is contrary to your assignment or not. Hint: it has to do with triangles, and it will work for any regular polygon with any number of sides :+)

The long decimals inside their formulas was from constants in their formulas which involved COT and TAN values.

C++ can do trig, just #include<cmath> So no need to hard code those values. But you can work out their value with code and make them a const variable.

Prefer to use double rather than float. It won't make any difference for this assignment, but it is a good habit to get into.

Good Luck !!