C Program to Find Roots of Quadratic Equation

calc_nPr.c

@@ -0,0 +1,42 @@
+#include <stdio.h>
+
+void main()
+{
+    int n, r, npr_var;
+
+    printf("Enter the value of n:");
+    scanf("%d", &n);
+    printf("\nEnter the value of r:");
+    scanf("%d", &r);
+
+    /* nPr is also known as P(n,r), the formula is:
+     * P(n,r) = n! / (n - r)! For 0 <= r <= n.
+     */
+    npr_var = fact(n) / fact(n - r);
+    printf("\nThe value of P(%d,%d) is: %d",n,r,npr_var);
+}
+// Function for calculating factorial
+int fact(int num)
+{
+    int k = 1, i;
+    // factorial of 0 is 1
+    if (num == 0)
+    {
+        return(k);
+    }
+    else
+    {
+        for (i = 1; i <= num; i++)
+    {
+            k = k * i;
+	}
+    }
+    return(k);
+}
+Output:
+
+Enter the value of n:
+5 
+Enter the value of r:
+2
+The value of P(6,2) is: 30

rootsofquad.c

@@ -0,0 +1,40 @@
+#include<stdio.h>
+#include<math.h>  // This is needed to use sqrt() function
+
+int main()
+{
+    printf("\n\n\t\tStudytonight - Best place to learn\n\n\n");
+    float a, b, c, determinant, r1, r2, real, imag;
+    printf("\n\nEnter coefficients a, b and c: \n\n\n");
+    scanf("%f%f%f", &a, &b, &c);
+
+    /*
+        mathematical formula to know the 
+        nature of the roots
+    */
+    determinant == b*b - 4*a*c; 
+
+    if(determinant > 0)    // both roots are real
+    {
+        r1 = (-b + sqrt(determinant))/2*a;  // Brackets are important
+        r2 = (-b - sqrt(determinant))/2*a;
+        printf("\n\n\nRoots are: %.2f and %.2f ", r1, r2);
+    }
+    else if(determinant == 0)   // both roots are real and equal
+    {
+        r1 = r2 = -b/(2*a); // brackets are important
+        printf("\n\n\nRoots are: %.2f and %.2f ", r1, r2);
+    }
+    /*
+        Determinant < 0 - both roots are imaginary of the 
+        form real + i*imaginary
+    */
+    else
+    {
+        real = -b/(2*a);
+        imag = sqrt(-determinant)/(2*a);
+        printf("\n\n\nRoots are %.2f + i%.2f and %.2f - i%.2f ", real, imag, real, imag);
+    }
+    printf("\n\n\n\n\t\t\tCoding is Fun !\n\n\n");
+    return 0;
+}