for loop cpp map

map<char,int> first;    first['a']=1;    first['b']=2;    first['c']=3;    first['d']=4;    first['e']=5;    first['a']=11;      //overrite 1    map<char,int>::iterator it;    for(it=first.begin();it!=first.end();++it){        cout<<it->first<<"="<<it->second<<endl;    }    typedef map<string,float> SFMap;    SFMap second;    second["abcdefg"]=3.1215926;    second["sdfsdf"]=234234;    second["sdfsdfdfdf"]=3219462;    for(SFMap::iterator it=second.begin();it!=second.end();++it){        cout<<it->first<<"="<<it->second<<endl;    }/*****************************************/// constructing maps#include <iostream>#include <map>using namespace std;bool fncomp (char lhs, char rhs) {return lhs<rhs;}struct classcomp {  bool operator() (const char& lhs, const char& rhs) const  {return lhs<rhs;}};int main (){  map<char,int> first;  first['a']=10;  first['b']=30;  first['c']=50;  first['d']=70;  map<char,int> second (first.begin(),first.end());  map<char,int> third (second);  map<char,int,classcomp> fourth;                 // class as Compare  bool(*fn_pt)(char,char) = fncomp;  map<char,int,bool(*)(char,char)> fifth (fn_pt); // function pointer as Compare  return 0;}