This commit is contained in:
bk2dcradle 2016-01-05 13:25:56 +05:30
parent 54c67dfb38
commit a5730e4ab9

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@ -809,7 +809,7 @@ void doSomethingWithAFile(const std::string& filename)
// object right at the location where it is invoked or passed as // object right at the location where it is invoked or passed as
// an argument to a function. // 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 // value of the pair
vector<pair<int, int> > tester; vector<pair<int, int> > tester;
@ -834,48 +834,22 @@ for(int i = 0; i < 3; i++){
dog_ids.push_back(i); dog_ids.push_back(i);
} }
int weight[3]; int weight[3] = {30, 50, 10};
weight[0] = 30, weight[1] = 50, weight[2] = 10;
// Say you want to sort dog_ids according to the dogs' weights // Say you want to sort dog_ids according to the dogs' weights
// So dog_ids should in the end become: [2, 0, 1] // So dog_ids should in the end become: [2, 0, 1]
// Here's where lambda expressions come in handy // 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]; 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 // lambda are really useful for the case of structs
// You can use lambda expressions instead of overloading // You can use lambda expressions instead of overloading
// the "<" operator // 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) // 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}; int arr[] = {1, 10, 3};
for(int elem: arr){ 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 // 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 example:
for(auto elem: arr) { 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 // Fun stuff
///////////////////// /////////////////////