replenish the code of previous commit.

ch03/ex3_21_pezy.cpp

@@ -0,0 +1,61 @@
+///
+///Redo the first exercise from § 3.3.3 (p. 105) using iterators.
+///
+
+#include <vector>
+#include <iterator>
+#include <string>
+#include <iostream>
+
+using std::vector;
+using std::string;
+using std::cout;
+using std::endl;
+
+void check(const vector<int>& vec)
+{
+  if (vec.empty())
+    cout << "size: 0; no values." << endl;
+  else
+  {
+    cout << "size: " << vec.size() << "; values:";
+    for (auto it = vec.begin(); it != vec.end(); ++it)
+      cout << *it << ",";
+    cout << "\b." << endl;
+  }
+}
+
+void check(const vector<string>& vec)
+{
+  if (vec.empty())
+    cout << "size: 0; no values." << endl;
+  else
+  {
+    cout << "size: " << vec.size() << "; values:";
+    for (auto it = vec.begin(); it != vec.end(); ++it)
+      if (it->empty()) cout << "(null)" << ",";
+      else cout << *it << ",";
+    cout << "\b." << endl;
+  }
+}
+
+int main()
+{
+  vector<int> v1;
+  vector<int> v2(10);
+  vector<int> v3(10, 42);
+  vector<int> v4{10};
+  vector<int> v5{10, 42};
+  vector<string> v6{10};
+  vector<string> v7{10, "hi"};
+
+  check(v1);
+  check(v2);
+  check(v3);
+  check(v4);
+  check(v5);
+  check(v6);
+  check(v7);
+
+  return 0;
+}

ch03/ex3_22.cpp

@@ -0,0 +1,30 @@
+///
+///Revise the loop that printed the first paragraph in text 
+///to instead change the elements in text that correspond 
+///to the first paragraph to all uppercase. 
+///After you’ve updated text, print its contents.
+///
+
+#include <iostream>
+#include <vector>
+#include <string>
+#include <iterator>
+
+using std::vector; using std::string; using std::cout; using std::cin; using std::endl;
+
+int main()
+{
+  vector<string> vec;
+  string str;
+  while (getline(cin, str))
+    if (!str.empty()) vec.push_back(str);
+
+  auto first = vec.begin();
+  for (auto& c : *first)
+    c = toupper(c);
+
+  for (auto it = vec.begin(); it != vec.end(); ++it)
+    cout << *it << endl;      
+
+  return 0;
+}

ch03/ex3_23.cpp

@@ -0,0 +1,23 @@
+///
+///Write a program to create a vector with ten int elements. 
+///Using an iterator, assign each element a value that is twice its current value.
+/// Test your program by printing the vector.
+///
+
+#include <vector>
+#include <iostream>
+#include <iterator>
+
+using std::vector; using std::iterator; using std::cout; using std::endl;
+
+int main()
+{
+  vector<int> ivec(10, 1);
+  for (auto it = ivec.begin(); it != ivec.end(); ++it)
+    *it *= 2;
+  for (auto value : ivec)
+    cout << value << " ";
+  cout << endl;
+
+  return 0;
+}