refactoring: factorial

src/main/c/Calculator/calculator.c

@@ -121,6 +121,13 @@ double getDoubleInput(const char *message) {
     scanf("%lf", &input);
     return input;
 }
+double factorial(double num) {
+    if (num == 0) {
+        return 1;
+    } else {
+        return num * factorial(num - 1);
+    }
+}
 
 int getIntInput(const char *message) {
     int input;