diff options
| -rw-r--r-- | c++.html.markdown | 48 |
1 files changed, 7 insertions, 41 deletions
diff --git a/c++.html.markdown b/c++.html.markdown index 6033ca06..c1bacf6a 100644 --- a/c++.html.markdown +++ b/c++.html.markdown @@ -809,7 +809,7 @@ void doSomethingWithAFile(const std::string& filename) // object right at the location where it is invoked or passed as // an argument to a function. -// Example consider sorting a vector of pairs using the second +// For example, consider sorting a vector of pairs using the second // value of the pair vector<pair<int, int> > tester; @@ -820,7 +820,7 @@ 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) { +sort(tester.begin(), tester.end(), [](const pair<int, int>& lhs, const pair<int, int>& rhs) { return lhs.second < rhs.second; }); @@ -834,48 +834,22 @@ for(int i = 0; i < 3; i++){ dog_ids.push_back(i); } -int weight[3]; -weight[0] = 30, weight[1] = 50, weight[2] = 10; +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) { +sort(dog_ids.begin(), dog_ids.end(), [&weight](const int &lhs, const int &rhs) { return weight[lhs] < weight[rhs]; }); -// Note we captured "weight" in the above example. +// Note we captured "weight" by reference in the above example. // lambda are really useful for the case of structs // You can use lambda expressions instead of overloading // the "<" operator -struct dog{ - int weight, age; -}dogs[3]; - -dogs[0].weight = 30, dogs[0].age = 4; -dogs[1].weight = 40, dogs[1].age = 10; -dogs[2].weight = 20, dogs[2].age = 9; - -// Say I want to sort the dogs array by the dogs' weights - -sort(dogs, dogs+3, [](const dog &lhs, const dog &rhs) { - return lhs.weight < rhs.weight; - }); -// dogs is now sorted according to their weight - -// Do something with the dogs - -// Now I want to sort the dogs by in descending order of their age - -sort(dogs, dogs+3, [](const dog &lhs, const dog &rhs) { - return lhs.age > rhs.age; - }); -// dogs is now sorted in descending order of their age - - /////////////////////////////// // Range For (C++11 and above) /////////////////////////////// @@ -884,24 +858,16 @@ sort(dogs, dogs+3, [](const dog &lhs, const dog &rhs) { int arr[] = {1, 10, 3}; for(int elem: arr){ - cout<<elem<<'\n'; + cout << elem << endl; } // You can use "auto" and not worry about the type of the elements of the container -// Caveat: Don't assign inside the range for loop // For example: for(auto elem: arr) { - elem = -1; + // Do something with each element of arr } -// "arr" remains unchanged - -// Why doesn't it change? -// What actually is happening is that the value of "arr[i]" is stored in -// the variable "elem" in every iteration. So assigning "elem" doesn't assign "arr[i]". -// For more, checkout: http://en.cppreference.com/w/cpp/language/range-for - ///////////////////// // Fun stuff ///////////////////// |