Finished ch09 🍻

ch09/README.md

@@ -273,3 +273,6 @@ what does numbers.find(name) return?
 string::npos
 
 ## [Exercise 9.49](ex9_49.cpp)
+## [Exercise 9.50](ex9_50.cpp)
+## [Exercise 9.51](ex9_51.cpp)
+## [Exercise 9.52](ex9_52.cpp)

ch09/ex9_52.cpp

@@ -0,0 +1,45 @@
+//
+//  ex9_52.cpp
+//  Exercise 9.52 
+//
+//  Created by pezy on 12/5/14.
+//  Copyright (c) 2014 pezy. All rights reserved.
+//
+//  @Brief  Use a stack to process parenthesized expressions. 
+//          When you see an open parenthesis, note that it was seen. 
+//          When you see a close parenthesis after an open parenthesis, 
+//          pop elements down to and including the open parenthesis off the stack. 
+//          push a value onto the stack to indicate that a parenthesized expression was replaced. 
+
+#include <stack>
+#include <string>
+#include <iostream>
+
+using std::string; using std::cout; using std::endl; using std::stack;
+
+int main()
+{
+    string expression{"This is (pezy)."};
+    bool bSeen = false;
+    stack<char> stk;
+    for (const auto &s : expression)
+    {
+        if (s == '(') { bSeen = true; continue; }
+        else if (s == ')') bSeen = false;
+
+        if (bSeen) stk.push(s);
+    }
+
+    string repstr;
+    while (!stk.empty())
+    {
+        repstr += stk.top();
+        stk.pop();
+    }
+
+    expression.replace(expression.find("(")+1, repstr.size(), repstr);
+
+    cout << expression << endl;
+
+    return 0;
+}