Algorithms
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Algorithms

The STL also provides some standard algorithms. There are way to many to list here, but they all work pretty much the same way. I have selected some random ones:

unsigned count(InIter first, InIter last, T value)

counts all elements in the range [first, last[ that match the given value.

FwdIter max_element(FwdIter first, FwdIter last)

returns an iterator that points to the larges element in the range [first,last[. (can you guess what min_element does?)

InIter find(InIter first, InIter last, T value)

returns an iterator to the first occurence of value in the range [first,last[.

void sort(RandIter first, RandIter last)

sorts the elements in [first,last[ to be ascending. The value type of the container must support the operator<

void random_shuffle(RandIter first, RandIter last)

randomly shuffles the elements in the range [first,last[.

count and find require an Input Iterator or better, maxElement requires a forward iterator or better, sort and random_shuffle require a random access iterator.

There are about 66 algorithm in the STL. For a complete reference, read Pg. 270-274 and Pg 328-369.

To use algorithms, you have to include the <algorithm>

I want you to know the five algorithms given here, If you need to know other ones then I'll provide the reference.

Example:

list<int> l;
l.push_back(1);
l.push_back(2);
l.push_back(1);
l.push_back(3);

// There are two 1's in there, so this will print 2
cout << count(l.begin(),l.end(),1) << endl;

Practice: Print out the value of the largest element in l.

cout << *(max_element(l.begin(),l.end()));

Here is another example:

vector<int> v;
for (int i=1;i<100;i++)
  v.push_back(i);

random_shuffle(v.begin(),v.end());

cout << "The largest element is now at ";
cout << max_element(v.begin(),v.end())-v.begin() << endl;