modified: learnc/a.exe

new file:   learnc/learnc12.c
	new file:   learnc/learnc13.c

learnc/learnc13.c

@@ -0,0 +1,25 @@
+#include <stdio.h>
+
+int factorial(int x);
+
+int main() {
+    /* testing code */
+    printf("0! = %i\n", factorial(0));
+    printf("1! = %i\n", factorial(1));
+    printf("3! = %i\n", factorial(3));
+    printf("5! = %i\n", factorial(5));
+}
+
+/* define your function here (don't forget to declare it) */
+int factorial(int x) {
+    
+    if (x == 0) {
+        
+        return 1;
+    } else if (x >= 1) {
+
+        return x*factorial(x-1);
+    }
+    
+    return 0;
+}