added 9.23 and improved 9.24

ch09/README.md

@@ -154,3 +154,11 @@ FIXED: (changed the `while` loop)
 ```
 while (iter++ != mid)
 ```
+
+## Exercise 9.23:
+>In the first program in this section on page 346, what would
+the values of val, val2, val3, and val4 be if c.size() is 1?
+
+same value that equal to the first element's.
+
+## [Exercise 9.24](ex9_24.cpp)

ch09/ex9_24.cpp

@@ -1,23 +1,18 @@
-//! @Alan
+//! @Alan @pezy
 //!
 //! Exercise 9.24:
 //! Write a program that fetches the first element in a vector using at,
 //! the subscript operator, front, and begin. Test your program on an empty vector.
 //!
 #include <iostream>
-#include <string>
 #include <vector>
-#include <deque>
-#include <list>
-
 
 int main()
 {
     std::vector<int> v;
-    std::cout
-                //<< v.at(0);   //an exception was thrown
-                    //<< v[0];                  //nothing happened
-                        //<<  v.front();        //nothing happened
-                            << *v.begin();      //nothing happened
+    std::cout << v.at(0);       // terminating with uncaught exception of type std::out_of_range
+    std::cout << v[0];          // Segmentation fault: 11
+    std::cout << v.front();     // Segmentation fault: 11
+    std::cout << *v.begin();    // Segmentation fault: 11
     return 0;
 }