[HELP] Program that checks conic section

How can I make a program that accepts equations then prints out if "CIRCLE", "ELLIPSE", "PARABOLA" or "HYPERBOLA". This is my first try. The problem is that!!! It won't work. I think this is my 3rd work.

When I enter x^2+y^2 it says ELLIPSE. Its supposed to be a CIRCLE

Quote:

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If x² and y² both have the same coefficients like x² + y² or 3x² + 3y², then it is a circle.

If x² and y² both have different coefficients that have the same sign, like 4x² + 9y², or x² + 16y², then it is an ellipse.

If x² and y² have different signs, like 25x² - 9y², or 16y² - x², then it is a hyperbola.

If the equation has either x² and y², but not both, then it is a parabola.

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Code:

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#include <ctype.h>#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int
main(void)
{
    char eq[256];
    bool x_exist = false, y_exist = false, neg_exist = false;
    int x, y;


    fgets(eq, 256, stdin);


    for (int i = 0, end = strlen(eq); i < end; i++)
    {
        if (eq[i] == 'x')
        {
            x_exist == true;
            if (eq[i - 1] == '-' && neg_exist == false)
            {
                x = 1;
                neg_exist = true;
            }
            else if (eq[i - 1] == '+')
                x = 1;
            else if (isdigit(eq[i - 1]))
            {
                x = atoi(&eq[i - 1]);
                if (eq[i - 1] == '-' && neg_exist == false)
                {
                    x = 1;
                    neg_exist = true;
                }
                else if (eq[i - 1] == '+')
                    x = 1;
            }
        }
        else if (eq[i] == 'y')
        {
            y_exist == true;
            if (eq[i - 1] == '-' && neg_exist == false)
            {
                y = 1;
                neg_exist = true;
            }
            else if (eq[i - 1] == '+')
                y = 1;
            else if (isdigit(eq[i - 1]))
            {
                y = atoi(&eq[i - 1]);
                if (eq[i - 1] == '-' && neg_exist == false)
                {
                    y = 1;
                    neg_exist = true;
                }
                else if (eq[i - 1] == '+')
                    y = 1;
            }
        }
    }


    if ((!y_exist && x_exist) || (y_exist && !x_exist))
        printf("PARABOLA");
    else if (x == y)
        printf("CIRCLE");
    else if (x != y)
        printf("ELLIPSE");
    else if (neg_exist)
        printf("HYPERBOLA");


    return 0;
}

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I'm also thinking that my way is not the best way because it uses TOO much conditions. I think...

You're confusing yourself by using x (in the expressions you type) as a variable that characterises a conic, and x (in your code) to be a coefficient. Similarly for y.

There is also the problem that your rules will not detect the fact that "4x^2 -4xy + 4y^2 = 3" describes an ellipse. Conics aren't necessarily symmetric around the x or y axis.

Quote:

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Originally Posted by grumpy

You're confusing yourself by using x (in the expressions you type) as a variable that characterises a conic, and x (in your code) to be a coefficient. Similarly for y.

There is also the problem that your rules will not detect the fact that "4x^2 -4xy + 4y^2 = 3" describes an ellipse. Conics aren't necessarily symmetric around the x or y axis.

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I know that it wont detect an equation like "4x^2 -4xy + 4y^2 = 3" the problem is that I don't know what to do. That is why I'm asking and I am not confused by using x as a variable and as a coefficient...

Write out EXACTLY how the different equations will be entered into the program, and I'll fix it, because I'm confused whether it will be using the '^' char (ie., 4x^2), or not (4x²).

Like this:
Ellipse: yadayadaya
Circle: yadayadayada
Parabola: yadayadayada
etc.

You are correct. Your logic is too Rube Goldberg.