Question

I have this simple program to count the word frequency:

#include <iostream>
#include <map>
#include <cctype>
#include <string>
using namespace std;
int main(void) {
  map<string, int> words;
  map<string, int>::iterator i;
string s;
while (cin >> s) {
    transform(s.begin(), s.end(), s.begin(), ::tolower);
words[s]++;
  }
for (i=words.begin(); i != words.end(); i++)
    cout << i->first << " " << i->second << endl;
return 0;

Now how do I make it to count line frequency instead of word frequency. Each line is separated by ‘\n’ new line character in the input.

Answer 1

If you want to count the total lines, then its very simple:

 size_t countLine = 0;
 while(std::getline(std::cin, s)) countLine++;

But if you really want to count frequency of same line, then in your code, replace

string s;

with

line s;

where line is defined as:

struct line : std::string
{
    friend std::istream & operator >> (std::istream &in, line &ln) 
    {
        return std::getline(in, ln);
    }
};

Or, you can make it generic:

template<typename CharT, typename Traits = std::char_traits<CharT>, typename Allocator = std::allocator<CharT>>
struct basic_line : public std::basic_string<CharT, Traits, Allocator>
{
    friend std::basic_istream<CharT, Traits> & operator >> (std::basic_istream<CharT, Traits > &in, basic_line<CharT, Traits, Allocator> &ln) 
    {
        return std::getline(in, ln);
    }
};

then define these typedefs:

typedef basic_line<char>    line;
typedef basic_line<wchar_t> wline;