added calc_nPr.c

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