Ejemplo 1 (ifstream, comentarios)

#include <iostream>
//#include <fstream>

using namespace std;

bool comment(string &s);

int main()
{
    string s;
    //fstream ci;
    //ci.open("text.txt");
    while(getline(cin,s)){
        if(!comment(s))
            cout<<s<<endl;
    }

}

bool comment(string &s){
    bool com=false;
    for(int i=0;i<s.size();i++){
        if(s[i]!=' ')
            if(s[i]=='#'){
                com=true;
                break;
            }
            else break;
    }
    return com;
}