Does anyone know how to insert names in alphabetical order into a c++ vector?

Question

I made this code but it doesn’t work right, it inserts in alphabetical order backwards.

void inserirNomeNaLista(vector<string> &lista)
{
    vector<string>::iterator itr;
    string nome;
    cout << "Digite o nome para ser inserido na lista: ";
    cin >> nome;

    if (lista.size() == 0)
    {
        lista.push_back(nome);
    }
    else
    {
        for (itr = lista.begin(); itr != lista.end(); itr++)
        {
            if (*itr > nome)
            {
                lista.insert(itr, nome);
            }
            break;
        }
    }
}

Answer 1

If you plan for your list to be ordered, the simplest way to do this is to directly use a std::set, which is ordered and does not allow duplicates. The code looks like this:

std::set<std::string> nomes;
nomes.insert("Pedro");
nomes.insert("Amanda");
nomes.insert("Maria");

for (auto& nome : nomes)
    std::cout << nome << std::endl; // Amanda, Maria, Pedro

(coliru)

However, if you want to keep using the std::vector, can search for the position if inserting using the std::lower_bound. But note that this function only works correctly in already ordered lists (binary search). Thus:

void sortedInsert(std::vector<std::string>& vec, std::string value) {
    auto it = std::lower_bound(vec.begin(), vec.end(), value);
    vec.insert(it, std::move(value));
}

std::vector<std::string> nomes;
sortedInsert(nomes, "Pedro");
sortedInsert(nomes, "Amanda");
sortedInsert(nomes, "Maria");

for (auto& nome : nomes)
    std::cout << nome << std::endl; // Amanda, Maria, Pedro

(coliru)
With a little more templates: (coliru)

Answer 2

I suggest you take a look at the standard STL algorithms. To solve this exact problem your already exists the lower_bound

#include <algorithm>

void inserirNomeNaLista(std::vector<string> &lista)
{
  std::string nome;
  std::cout << "Digite o nome para ser inserido na lista: ";
  std::cin >> nome;

  typedef std::vector<std::string>::iterator VecIter;
  VecIter itr = std::lower_bound(lista.begin(), lista.end(), nome);    
  lista.insert(itr, nome);
}

It searches a sequence (pair of iterators) at the point where an item should be inserted so that the sequence is in ascending order. It is efficient because it performs binary search, but only works if the sequence is always ordered. But if you only use it to insert elements into one vector there is no problem, because in this case the insertions will always be in order.

---

Now if this is an exercise, and you can’t use the standard algorithms, I believe your error is the position of break, as already explained nthe comment of Luiz Vieira.

Answer 3

Friend, the STL already provides the Sort() method for you. It lexicographically analyzes the strings and sorts them. Here’s an example.

#include <algorithm> //Para o sort()
#include <iostream> //Para o cout
#include <vector>  //Para o vector<>()
#include <string> //Para a string

int main() {
    std::vector<std::string> v;
    v.push_back("bac"); v.push_back("abc"); v.push_back("cab"); v.push_back("cba");
    std::sort(v.begin(),v.end());
    for(int i = 0; i < v.size(); i++) std::cout << v[i] << std::endl;
}