Write a program to determine the roots of a quadratic equation.

Dr. A.P.J. Abdul Kalam Technical University, Lucknow

KCS151 / KCS251 Programming for Problem Solving - Using C Language

Lab Exercises

3. Write a program to determine the roots of a quadratic equation.

/*

 File: Prgrm03.c

 Author: Aditya Saini

 Date: Jan 15, 2021

 Description: Program to determine the roots of a quadratic equation.

*/

#include <stdio.h>

#include <math.h>

int main (void)

{

     double a, b, c;

     double dis;

     double root_1, root_2, real, img;

     //Input a, b and c for eq. ax²+bx+c = 0.

     printf ("For eq. ax^2 + bx + c = 0\n");

     printf ("Input a: ");

     scanf ("%lf", &a);

     printf ("Input b: ");

     scanf ("%lf", &b);

     printf ("Input c: ");

     scanf ("%lf", &c);

     //Calculate discriminant = b²-4ac

     dis = b * b - 4 * a * c;

     //If roots are real and different

     if (dis > 0)

     {

          root_1 = (-b + sqrt (dis)) / (2 * a);

          root_2 = (-b - sqrt (dis)) / (2 * a);

          printf ("First Root = %.2lf\n", root_1);

          printf ("Second Root = %.2lf", root_2);

     }

     //If roots are real and equal

     else if (dis == 0)

     {

          root_1 = root_2 = -b / (2 * a);

          printf ("First Root = Second Root = %.2lf", root_1);

     }

     //If roots are imaginary

     else

     {

          real = -b / (2 * a);

          img = sqrt (-dis) / (2 * a);

          printf ("First Root = %.2lf + %.2lfi\n", real, img);

          printf ("Second Root = %.2lf - %.2lfi", real, img);

     }

     return 0;

};

Output

For eq. ax^2 + bx + c = 0

Input a: 1

Input b: 2

Input c: 3

First Root = -1.00 + 1.41i

Second Root = -1.00 - 1.41i