Getting the width of a line from a file

[ajay16oct]

Hi everbody
i wantto get the width of a line from a file.somehow i got this code
#include <vector>
#include <string>
#include <fstream>
#include <iostream>
#include <cmath>
using namespace std;

int main(int argc, char* argv[]) {
ifstream in(argv[1]);
string line;
vector<string> lines;
while(getline(in, line)) // Read in entire file
lines.push_back(line);
if(lines.size() == 0) return 0;
int num = 0;
// Number of lines in file determines width:
const int width = int(log10(lines.size())) + 1;
for(int i = 0; i < lines.size(); i++) {
cout.setf(ios::right, ios::adjustfield);
cout.width(width);
cout << ++num << ") " << lines[i] << endl;
}
}

I cant understand the logic behing the BOLD and UNDERLINED statement ..Plz if anyone can let me know how its working
help would be appreciated.

[helios]

It's not getting the width of any line. It's taking the size of 'lines', which is a vector, and figuring out how many digits the decimal representation of that value uses.
Another way a little easier to understand (and probably even faster) is to repeatedly divide by 10.