add c++11 (#87)

* binary search c++

* selection sort c++11

* c++ recursive countdown

* c++ recursion

* c++ quicksort

* rename folder names to c++11

* add another version of binary_search function

* c++11 hash tables

* c++11 breadth-first search

03_recursion/c++11/01_countdown.cpp

@@ -0,0 +1,18 @@
+#include <iostream>
+
+using std::cout;
+using std::endl;
+
+void countdown(const int& i) {
+    cout << i << endl;
+    
+    // base case
+    if (i <= 0) return;\
+    
+    // recursive case
+    countdown(i - 1);
+}
+
+int main() {
+    countdown(5);
+}