C<T> c; // creates an empty container// c2 must be same type as c1C<T> c1(c2); // copies elements from c2 into c1// b and e are iterators denoting a sequenceC<T> c(b, e); // copies elements from the sequence into c

map<string, int> word_count; // empty map from string to int

// get an iterator to an element in word_countmap<string, int>::iterator map_it = word_count.begin();// *map_it is a reference to a pair<const string, int> objectcout << map_it->first; // prints the key for this elementcout << " " << map_it->second; // prints the value of the elementmap_it->first = "new key"; // error: key is const++map_it->second; // ok: we can change value through an iterator

map <string, int> word_count; // empty map// insert default initialzed element with key Anna; then assign 1to its valueword_count["Anna"] = 1;

// count number of times each word occurs in the inputmap<string, int> word_count; // empty map from string to intstring word;while (cin >> word)    ++word_count[word];

// if Anna not already in word_count, inserts new element with value1word_count.insert(map<string, int>::value_type("Anna", 1));

word_count.insert(make_pair("Anna", 1));

typedef map<string,int>::value_type valType;word_count.insert(valType("Anna", 1));

map<string, int> word_count; // empty map from string to intstring word;while (cin >> word) {    // inserts element with key equal to word and value 1;    // if word already in word_count, insert does nothing    pair<map<string, int>::iterator, bool> ret =    word_count.insert(make_pair(word, 1));    if (!ret.second) // word already in word_count        ++ret.first->second; // increment counter}

map<string,int> word_count;int occurs = word_count["foobar"];

int occurs = 0;if (word_count.count("foobar"))occurs = word_count["foobar"];

int occurs = 0;map<string,int>::iterator it = word_count.find("foobar");if (it != word_count.end())    occurs = it->second;

// erase of a key returns number of elements removedif (word_count.erase(removal_word))cout << "ok: " << removal_word << " removed\n";else cout << "oops: " << removal_word << " not found!\n";

// get iterator positioned on the first elementmap<string, int>::const_iteratormap_it = word_count.begin();// for each element in the mapwhile (map_it != word_count.end()) {    // print the element key, value pairs    cout << map_it->first << " occurs "    << map_it->second << " times" << endl;    ++map_it; // increment iterator to denote the next element}

/** A program to transform words.* Takes two arguments: The first is name of the word transformationfile* The second is name of the input to transform*/int main(int argc, char **argv){    // map to hold the word transformation pairs:    // key is the word to look for in the input; value is word to use    in the output    map<string, string> trans_map;    string key, value;    if (argc != 3)        throw runtime_error("wrongnumber of arguments");        // open transformation file and check that open succeeded    ifstream map_file;    if (!open_file(map_file, argv[1]))        throw runtime_error("no transformation file");        // read the transformation map and build the map     while (map_file >> key >> value)        trans_map.insert(make_pair(key, value));    // ok, now we‘re ready to do the transformations    // open the input file and check that the open succeeded    ifstream input;    if (!open_file(input, argv[2]))        throw runtime_error("no input file");    string line; // hold each line from the input    // read the text to transform it a line at a time    while (getline(input, line)) {        istringstream stream(line); // read the line a word at atime        string word;        bool firstword = true; // controls whether a space is printed        while (stream >> word) {        // ok: the actual mapwork, this part is the heart of the program        map<string, string>::const_iterator map_it =        trans_map.find(word);        // if this word is in the transformation map        if (map_it != trans_map.end())        // replace it by the transformation value in the map            word = map_it->second;        if (firstword)            firstword = false;        else            cout << " "; // print space between words            cout << word;        }        cout << endl; // done with this line of input    }    return 0;}

// define a vector with 20 elements, holding two copies of each number//from 0 to 9vector<int> ivec;for (vector<int>::size_type i = 0; i != 10; ++i) {    ivec.push_back(i); // duplicate copies of each number}// iset holds unique elements from ivecset<int> iset(ivec.begin(), ivec.end());cout << ivec.size() << endl; // prints 20cout << iset.size() << endl; // prints 10

set<string> set1; // empty setset1.insert("the"); // set1 now has one elementset1.insert("and"); // set1 now has two elements

set<int> iset2; // empty setiset2.insert(ivec.begin(), ivec.end()); // iset2 has 10elements

void restricted_wc(ifstream &remove_file,map<string, int> &word_count){    set<string> excluded; // set to hold words we‘ll ignore    string remove_word;    while (remove_file >> remove_word)        excluded.insert(remove_word);    // read input and keep a count for words that aren‘t in theexclusion set    string word;    while (cin >> word)    // increment counter only if the word is not in excluded        if (!excluded.count(word))            ++word_count[word];}

// adds first element with key Barthauthors.insert(make_pair(string("Barth, John"),string("Sot-Weed Factor")));// ok: adds second element with key Barthauthors.insert(make_pair(string("Barth, John"),string("Lost in the Funhouse")));

multimap<string, string> authors;string search_item("Kazuo Ishiguro");// erase all elements with this key; returns number of elements removedmultimap<string, string>::size_type cnt =authors.erase(search_item);

// author we‘ll look forstring search_item("Alain de Botton");// how many entries are there for this authortypedef multimap<string, string>::size_type sz_type;sz_type entries = authors.count(search_item);// get iterator to the first entry for this authormultimap<string,string>::iterator iter =authors.find(search_item);// loop through the number of entries there are for this authorfor (sz_type cnt = 0; cnt != entries; ++cnt, ++iter) cout <<    iter->second << endl; // print each title

// definitions of authors and search_item as above// beg and end denote range of elements for this authortypedef multimap<string, string>::iterator authors_it;authors_it beg = authors.lower_bound(search_item),end = authors.upper_bound(search_item);// loop through the number of entries there are for this authorwhile (beg != end) {    cout << beg->second << endl; // print each title    ++beg;}

// definitions of authors and search_item as above// pos holds iterators that denote range of elements for this keypair<authors_it, authors_it>pos = authors.equal_range(search_item);// loop through the number of entries there are for this authorwhile (pos.first != pos.second) {    cout << pos.first->second << endl; // print each title    ++pos.first;}

class TextQuery {public:    // typedef to make declarations easier    typedef std::vector<std::string>::size_type line_no;    /* interface:    * read_file builds internal data structures for the given file    * run_query finds the given word and returns set of lines on    which it appears    * text_line returns a requested line from the input file    */    void read_file(std::ifstream &is)    { store_file(is); build_map(); }    std::set<line_no> run_query(const std::string&) const;    std::string text_line(line_no) const;private:    // utility functions used by read_file    void store_file(std::ifstream&); // store input file    void build_map(); // associated each word with a set of line    numbers    // remember the whole input file    std::vector<std::string> lines_of_text;    // map word to set of the lines on which it occurs    std::map< std::string, std::set<line_no> > word_map;};

// program takes single argument specifying the file to queryint main(int argc, char **argv){    // open the file from which user will query words    ifstream infile;    if (argc < 2 || !open_file(infile, argv[1])) {        cerr << "No input file!" << endl;        return EXIT_FAILURE;    }    TextQuery tq;    tq.read_file(infile); // builds query map    // iterate with the user: prompt for a word to find and print results    // loop indefinitely; the loop exit is inside the while    while (true) {        cout << "enter word to look for, or q to quit: ";        string s;        cin >> s;        // stop if hit eof on input or a ‘q‘is entered        if (!cin || s == "q") break;        // get the set of line numbers on which this word appears        set<TextQuery::line_no> locs = tq.run_query(s);        // print count and all occurrences, if any        print_results(locs, s, tq);    }    return 0;}