/*
 *  Dato: 13-10-2011
 *  Kursus: Imperativ Programming
 *  Underviser: Kurt Nørmark
 *  Opgave: http://people.cs.aau.dk/%7Enormark/impr-c/functions-anden-grads-ex-pars-slide-exercise-1.html
 *  Tid brugt: 75 minutter
 */

#include <stdio.h>
#include <math.h>

// Prototyper.
double findDiscriminant(double a, double b, double c);
double findRootOne(double a, double b, double discriminant);
double findRootTwo(double a, double b, double discriminant);
void solveQuadraticEquation(double a, double b, double c);

// Main call.
int main(void) {
    // Initialize variables
    int a,b,c;

    // Start do while loop, if a,b,c are NOT zero continue running the loop
    do {
        // Get values.
        printf("Write values for a, b and c> ");
        scanf("%d %d %d", &a, &b, &c);

        // If a is zero it's not a quadratic equation, but that's no reason to quit.
        if (a == 0) {
            continue;
        }
        else {
            solveQuadraticEquation(a,b,c);
        }
    }
    while (!(a == 0 && b == 0 && c == 0));
    return 0;
}

// Solve quadratic equation. Could just move this into main, but assignment said to call it.
void solveQuadraticEquation(double a, double b, double c) {
    if (findDiscriminant(a,b,c) < 0) {
        printf("No roots\n");
    }
    else {
        printf("The first root: %.2f\n", findRootOne(a,b, findDiscriminant(a,b,c)));
        printf("The second root: %.2f\n", findRootTwo(a,b, findDiscriminant(a,b,c)));
    }
}

// Find discriminant.
double findDiscriminant(double a, double b, double c) {
    return b * b - 4 * a * c;
}

// Find the first root if it exists.
double findRootOne(double a, double b, double discriminant) {
    // if the discriminant is 0 then we use a special case.
    if (discriminant == 0) {
        return -b / (2*a);
    }
    // Otherwise use this.
    else {
        return (-b + sqrt(discriminant)) / (2*a);
    }
}

// Find the second root if it exists.
double findRootTwo(double a, double b, double discriminant) {
    // Get the second root
    if (discriminant > 0) {
        return (-b - sqrt(discriminant)) / (2*a);
    }
    // If it doesn't exist, set it to the same value as the first root.
    else {
        return (-b + sqrt(discriminant)) / (2*a);
    }
}