Implement recursive factorial calculation

factorial_recursive.c

@@ -0,0 +1,43 @@
+#include <stdio.h>
+
+/*
+  Calculates the factorial of a non-negative integer n recursively.
+  The factorial of n (n!) is the product of all positive integers less than or
+  equal to n. This function uses the recursive definition:
+  - Base Case: factorial(0) = 1
+  - Recursive Step: factorial(n) = n * factorial(n - 1) for n > 0
+ */
+
+long long factorial(int n) {
+    if (n < 0) {
+        return -1;
+    }
+
+    // Base Case: Stop condition for the recursion. Factorial of 0 is 1.
+    if (n == 0) {
+        return 1;
+    }
+
+    // Recursive Step: The function calls itself with a smaller argument (n - 1).
+    return (long long)n * factorial(n - 1);
+}
+
+int main() {
+    int number;
+    long long result;
+
+    printf("Enter a non-negative integer (up to 20 for accurate results): ");
+    if (scanf("%d", &number) != 1) {
+        printf("Invalid input. Please enter a number.\n");
+        return 1;
+    }
+    result = factorial(number);
+
+    // Check for error conditions 
+    if (result == -1) {
+        printf("Error: Factorial is not defined for negative numbers.\n");
+    } else {
+        printf("The factorial of %d is: %lld\n", number, result);
+    }
+    return 0; 
+}