Add chapter 13 Exercise

thinkcspy/Chapter-13-Exercises/readposint.py

@@ -0,0 +1,11 @@
+def readposint(num):
+    try:
+        val = int(num)
+        if val > 0:
+            print("You entered '{}'.".format(val))
+        else:
+            print("'{}' is not a positive.".format(val))
+    except Exception:
+        print("'{}' is not a number.".format(num))  
+
+readposint(input("Please enter a positive number: "))