added drill13 for chapter13

Author: trapperdot00

Chapter13/README.md

@@ -40,3 +40,6 @@ Make the cosine blue.
 
 ## [Drill 12](drill/12)
 Write a function `sloping_cos()` that adds a cosine to `slope()` (as defined above) and add it to the window.
+
+## [Drill 13](drill/13)
+Define a `struct Person` containing a `string` name and an `int` age.

Chapter13/drill/13/Person.h

@@ -0,0 +1,11 @@
+#ifndef PERSON_H
+#define PERSON_H
+
+#include <string>
+
+struct Person {
+	std::string name;
+	int age;
+};
+
+#endif