Why am I getting a segmentation error? What is the reason getting output as numbers instead of strings?

I am aware of why segmentation faults occur, but I am not able to find out the error with the following code I made to split a string on the basis of whitespaces.

#include<iostream>
#include<string>
#include<vector>
#include<typeinfo>
using namespace std;
vector<string> split(const string& s)
{
    //cout << "HERE";
    vector<string> tab;
    for(unsigned int a = 0; a < s.size(); a++)
    {
        string temp = to_string(s[a]);
        while(to_string(s[a]) != " ")
        {
            a++;
            temp = temp + s[a];
        }
        tab.push_back(temp);
    }
    return tab;
}   


int main()
{
    int n;
    cin >> n;

    while(n--)
    {
        string s;
        cin >> s;
        vector<string> temp = split(s);
        for(unsigned int i = 0; i < temp.size(); i++)
        {
            cout << temp[i] << endl;
        }
    }
    return 0;
}

Also, if I comment out the while loop in the split function, I get numbers when I print out the resulting strings. Is it because of to_string? If I use typeid(variable).name() on the resulting strings that I get when I am printing them in the main function,this is what I get : NSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE