Merge pull request #1887 from bk2dcradle/master

[c++/en] Added Lambda Expressions and Range for

c++.html.markdown

@@ -820,6 +820,76 @@ std::map<Foo, int, compareFunction> fooMap;
 fooMap[Foo(1)]  = 1;
 fooMap.find(Foo(1)); //true
 
+///////////////////////////////////////
+// Lambda Expressions (C++11 and above)
+///////////////////////////////////////
+
+// lambdas are a convenient way of defining an anonymous function
+// object right at the location where it is invoked or passed as 
+// an argument to a function.
+
+// For example, consider sorting a vector of pairs using the second 
+// value of the pair
+
+vector<pair<int, int> > tester;
+tester.push_back(make_pair(3, 6));
+tester.push_back(make_pair(1, 9));
+tester.push_back(make_pair(5, 0));
+
+// Pass a lambda expression as third argument to the sort function
+// sort is from the <algorithm> header
+
+sort(tester.begin(), tester.end(), [](const pair<int, int>& lhs, const pair<int, int>& rhs) {
+        return lhs.second < rhs.second;
+    });
+
+// Notice the syntax of the lambda expression,
+// [] in the lambda is used to "capture" variables
+// The "Capture List" defines what from the outside of the lambda should be available inside the function body and how.
+// It can be either:
+//     1. a value : [x]
+//     2. a reference : [&x]
+//     3. any variable currently in scope by reference [&]
+//     4. same as 3, but by value [=]
+// Example:
+
+vector<int> dog_ids;
+// number_of_dogs = 3;
+for(int i = 0; i < 3; i++) {
+	dog_ids.push_back(i);  
+}
+
+int weight[3] = {30, 50, 10};
+
+// Say you want to sort dog_ids according to the dogs' weights
+// So dog_ids should in the end become: [2, 0, 1]
+
+// Here's where lambda expressions come in handy
+
+sort(dog_ids.begin(), dog_ids.end(), [&weight](const int &lhs, const int &rhs) {
+        return weight[lhs] < weight[rhs];
+    });
+// Note we captured "weight" by reference in the above example.
+// More on Lambdas in C++ : http://stackoverflow.com/questions/7627098/what-is-a-lambda-expression-in-c11
+
+///////////////////////////////
+// Range For (C++11 and above)
+///////////////////////////////
+
+// You can use a range for loop to iterate over a container
+int arr[] = {1, 10, 3};
+
+for(int elem: arr){
+	cout << elem << endl;
+}
+
+// You can use "auto" and not worry about the type of the elements of the container
+// For example:
+
+for(auto elem: arr) {
+	// Do something with each element of arr
+}
+
 /////////////////////
 // Fun stuff
 /////////////////////