C program to find the roots of a quadratic equation

Comprehensive Collection of C Programming Examples

In this example, you will learn how to find the roots of a quadratic equation in C programming.

To understand this example, you should understand the followingC programmingTopic:

• C programming operators

• C if ... else statement

The standard form of a quadratic equation is:

ax2　+　bx　+　c = 0, when
a, b and c are real numbers,
a != 0

b²-4acThe term is called the discriminant of a quadratic equation. It describes the nature of the roots.

• If the discriminant is greater than 0, the roots are different real numbers

• If the discriminant is equal to 0, then the roots are real and equal.

• If the discriminant is less than 0, then the roots are different complex numbers.

Program to find the roots of a quadratic equation

#include <math.h>
#include <stdio.h>
int main() {
　　　　double a, b, c, discriminant, root1, root2, realPart, imagPart;
　　　　printf("Input coefficients a, b and c: ");
　　　　scanf("%lf %lf %lf", &a, &b, &c);
　　　　discriminant = b　*　b　-　4　*　a　*　c;
　　　　//　The condition for unequal real roots
　　　　if (discriminant > 0) {
　　　　　　　　root1　= (-b　+　sqrt(discriminant))　/　(2　*　a);
　　　　　　　　root2　= (-b　-　sqrt(discriminant))　/　(2　*　a);
　　　　　　　　printf("root1　= %.2lf and root2　= %.2lf", root1, root2);
　　　　}
　　　　//　The condition for equal real roots
　　　　else if (discriminant == 0) {
　　　　　　　　root1　= root2　=　-b　/　(2　*　a);
　　　　　　　　printf("root1　= root2　= %.2lf;", root1);
　　　　}
　　　　//　If the root is not a real number
　　　　else {
　　　　　　　　realPart =　-b　/　(2　*　a);
　　　　　　　　imagPart = sqrt(-discriminant)　/　(2　*　a);
　　　　　　　　printf("root1　= %.2lf+%.2lfi and root2　= %.2f-%.2fi
　　　　}
　　　　return 0;
}

Output Result

Enter coefficients a, b, and c:　2.3
4
5.6
root1　=　-0.87+1.30i and root2　=　-0.87-1.30i

In this program, the sqrt() library function is used to find the square root of a number. For more information, please visit:sqrt() Function.

Comprehensive Collection of C Programming Examples