ShoppingList, C++ (gcc)

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//g++  7.4.0
//Shopping list: important map container functions in action

//this code is created by Rezaul Hoque on August 01,2021;contact: jewelmrh@yahoo.com

//note: codes shared by Rezaul Hoque on rextester are not for sale; they are created and shared to facilitate the algorithm learning process; many like Hoque use this platform to practice programming ;Rezaul hopes his contribution helps others to fine tune their learning;

#include <iostream>
#include <map>
#include <string>
using namespace std;
int main(){
//here in creating the map object,3 parameters are used; first one is the key type,second one is the data type and the third one is the comparison type that will order the list from least to great keys; note this less<comparison type> is the default
map<int,string,less<int>> list;
// use of map "[ ]" operator
list[3]="soap";
list[2]="toothpaste";
list[1]="comb";
//use of map emplace() and map emplace_hint()
list.emplace(5,"cooking oil");
list.emplace(4,"milk");
list.emplace(6,"fish");
list.emplace(7,"lentils");
list.emplace(8,"snake gourd");
list.emplace(9,"potato");
auto it=list.end();
list.emplace_hint (it,10,"puffed rice");
list.emplace_hint(it,11,"peanut");
list.emplace_hint(it,12,"jaggery");
cout<< "The shopping list looks like:\n";
for(auto& x: list)
cout<<x.first<<" : "<<x.second<<"\n";
//use of map size()
cout<<"\nThere are "<<list.size()<<" elements left.\n";
cout<<"The list is based on priority of making a visit to the respective shop: first grocery, then kitchem market and finally the street snack vendor.\n";
cout<<"If the priority were reversed (first go to the snack vendor and finally to the grocery), the list would look like:\n";
//use of map rbegin() and rend()
for(map<int,string>::reverse_iterator it=list.rbegin(); it!=list.rend();++it)
cout<<it->first<<" => "<<it->second<<" \n";
cout<<"But let's stick to the original list and start our shopping.\n";
cout<<"\n After paying visit to grocery the list looks like:\n" ;
//use of map erase()
list.erase(1);
list.erase(2);
list.erase(3);
for(auto& x: list)
cout<<x.first<<" : "<<x.second<<"\n";
cout<<"\nThere are "<<list.size()<<" elements left.\n";
cout<<"After paying a visit to the vegetable market the list looks like:\n" ;
//use of map lower_bound() and upper_bound() to delete a range
map<int,string>::iterator low,up;
low=list.lower_bound(4);
up = list.upper_bound(9);
list.erase (low,up);
for(auto& x: list)
cout<<x.first<<" : "<<x.second<<"\n";
cout<<"\There are "<<list.size()<<" elements left.\n";
cout<<"\nAfter paying visit to street snack vendor the list looks like:\n" ;
list.erase(10);
list.erase(11);
list.erase(12);
for(auto& x: list)
cout<<x.first<<" : "<<x.second<<"\n";
cout<<"\There are "<<list.size()<<" elements left.\n";
return 0;
}

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Compilation time: 0.62 sec, absolute running time: 0.15 sec, cpu time: 0.01 sec, memory peak: 5 Mb, absolute service time: 0,87 sec