C++ Multimap Printing - c++

Question

I'm trying to make a name, and then give a list of courses this person has taken. Here is my code currently:
#include <iostream>
#include <string>
#include <map>
#include <list>
using namespace std;
int main()
{
multimap<string,string> students;
students.insert(make_pair("john","cs1"));
students.insert(make_pair("john","cs2"));
for (auto itr = students.begin(); itr != students.end(); ++itr)
{
cout << itr->first << '\t' << itr->second << '\n';
}
}
This prints out:
John CS1
John CS2
If I wanted to make it print out the first value and then print out all second values, how would I do this? Do I need to use a list as the second value or something? Or is this doable with just multimaps? For example:
John CS1 CS2

Answer 1

You can use equal_range to achieve what you wanted, see:
std::string current_key = "";
for (auto itr = students.begin(); itr != students.end(); ++itr)
{
if(current_key == itr->first) {
continue;
} else {
current_key = itr->first;
}
const auto result = students.equal_range(itr->first);
cout << itr->first << ": ";
for(auto it = result.first; it != result.second; ++it) {
cout << it->second << " ";
}
cout << endl;
}
See working example here: https://ideone.com/RqCFOk

Answer 2

You'll may eventually end up creating a class to model a student, in the meantime, you could just iterate over the multimap container and check if the current key is the same as the previous:
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <string>
using students_t = std::multimap<std::string, std::string>;
void print_students_list(students_t const& students)
{
// Start printing the name of the first student and the first course (the first key-value
// pair) if the container is not empty.
auto student{ students.cbegin() };
if ( student == students.cend() )
return;
std::cout << std::setw(12) << std::left << student->first
<< std::setw(8) << student->second;
// Then iterate over the rest of the container printing the name (after a newline)
// only if it's different from the previous one.
for ( auto prev{ student++ }; student != students.cend(); prev = student, ++student )
{
if ( student->first != prev->first )
std::cout << '\n' << std::setw(12) << student->first;
std::cout << std::setw(8) << student->second;
}
std::cout << '\n';
}
int main()
{
students_t students {
{"john", "cs1"},
{"john", "cs2"},
{"Karen", "cs2"},
{"Karen", "nc1"},
{"Karen", "nc2"},
{"Bob", "nc1"}
};
print_students_list(students);
}