added exercise01 to chapter13

Author: trapperdot00

Chapter13/README.md

@@ -110,3 +110,5 @@ Why would you format your input rather than just having the file contain "the nu
 
 ## [Review 14](review/14.txt)
 How do you plan the general layout of a graph? How do you reflect that layout in your code?
+
+## [Exercise 1](exercise/01/01.cpp)

Chapter13/exercises/01/01.cpp

@@ -0,0 +1,25 @@
+#include <iostream>
+
+// I think this is more readable
+int iterative_fac(int n) {
+	int j = 1;
+	while (n > 1)
+		j *= n--;
+	return j;
+}
+
+// This is cooler though
+int recursive_fac(int n) {
+	return n > 1 ? n * recursive_fac(n-1) : 1;
+}
+
+int main() {
+	for (int i = 0; i < 21; ++i) {
+		std::cout << i
+			<< "! == "
+			<< recursive_fac(i)
+			<< " (recursive) == "
+			<< iterative_fac(i)
+			<< " (iterative)\n";
+	}
+}