Update code.md

Author: ethan42

code.md

@@ -211,4 +211,35 @@ int main() {
 }
 ```
 
+## Υπολογισμός παραγοντικού / factorial - χρήση αναδρομής - lec11
+
+Credits: Στέφανος
+
+```c
+/* Short program for computing the factorial
+   of a number. Does not handle edge-cases
+   like negative numbers. */
+#include <stdio.h>
+#include <stdlib.h>
+
+int factorial(int num) {
+  printf("Computing: factorial(%d)\n", num);
+  if (num <= 1) {
+    return 1;
+  } else {
+    return num * factorial(num - 1);
+  }
+}
+
+int main(int argc, char ** argv) {
+  if (argc != 2) {
+    printf("Run this program as ./factorial <num>\n");
+    return 1;
+  }
+  int num = atoi(argv[1]);
+  printf("The factorial of this number is: %d\n", factorial(num));
+  return 0;
+}
+```
+