Example: Solve Quadratic Equation Using Function in C

// Solve Quadratic Equation Using Function
#include <stdio.h>
#include <math.h> // Required for sqrt() function

// Function to calculate and print roots of a quadratic equation
void findRoots(double a, double b, double c) {
    double discriminant, root1, root2, realPart, imagPart;

    // Step 1: Calculate the discriminant
    discriminant = b * b - 4 * a * c;

    // Step 2: Check the value of the discriminant and calculate roots accordingly
    if (discriminant > 0) {
        // Case 1: Discriminant is positive (two distinct real roots)
        root1 = (-b + sqrt(discriminant)) / (2 * a);
        root2 = (-b - sqrt(discriminant)) / (2 * a);
        printf("Roots are real and distinct.\n");
        printf("Root 1 = %.2lf\n", root1);
        printf("Root 2 = %.2lf\n", root2);
    } else if (discriminant == 0) {
        // Case 2: Discriminant is zero (two identical real roots)
        root1 = root2 = -b / (2 * a);
        printf("Roots are real and identical.\n");
        printf("Root 1 = Root 2 = %.2lf\n", root1);
    } else {
        // Case 3: Discriminant is negative (two complex conjugate roots)
        realPart = -b / (2 * a);
        imagPart = sqrt(-discriminant) / (2 * a);
        printf("Roots are complex and conjugate.\n");
        printf("Root 1 = %.2lf + %.2lfi\n", realPart, imagPart);
        printf("Root 2 = %.2lf - %.2lfi\n", realPart, imagPart);
    }
}

int main() {
    double a, b, c;

    // Step 1: Get coefficients from the user
    printf("Enter coefficient a: ");
    scanf("%lf", &a);
    printf("Enter coefficient b: ");
    scanf("%lf", &b);
    printf("Enter coefficient c: ");
    scanf("%lf", &c);

    // Step 2: Handle the case where 'a' is zero (not a quadratic equation)
    if (a == 0) {
        printf("Coefficient 'a' cannot be zero for a quadratic equation.\n");
        // If a=0, it's a linear equation: bx + c = 0 => x = -c/b
        if (b != 0) {
            printf("It's a linear equation. Root x = %.2lf\n", -c / b);
        } else if (c == 0) {
            printf("Infinite solutions (0 = 0).\n");
        } else {
            printf("No solution (0 = -c, where c is non-zero).\n");
        }
    } else {
        // Step 3: Call the function to find and print the roots
        findRoots(a, b, c);
    }

    return 0;
}