Converting a Greek string of letters to all lower case

[jasongog24]

So, I am trying to code a console program in Greek, and since I want to make the input non case sensitive, I wanted to create a function that converts all Greek letters of a string (Upper letters, Lower toned[accentuated] letters and Upper toned letters) into lower letters. I tried using maps to cross reference between strings, as well as check if it is toned/untoned lower/upper case letter (since they are not in order within UTF) Here's what I've attempted thus far

#include<iostream>
#include<windows.h>
#include<map>

using namespace std;

string sLower = " αβγδεζηθικλμνξοπρστυφχψω";
string sUpper = " ΑΒΓΔΕΖΗΘΙΚΛΜΝΞΟΠΡΣΤΥΦΧΨΩ";
string sTLower = " άέήίόύώ";
string sTUpper = " ΆΈΉΊΌΎΏ";

string matchCase (string a){

map<char, bool> greekLower, uCheck, UTcheck, ltcheck;
map<char, char> greekUpper, greekTLower, greekTUpper;

string answer;

for (int i=1; i<=24; i++){
    greekLower[sLower[i]] = true;
    greekUpper[sUpper[i]] = greekLower[i];
    uCheck[sUpper[i]] = true;
}
greekTLower['ά'] = greekTUpper['Ά'] = sLower[1];
greekTLower['έ'] = greekTUpper['Έ'] = sLower[5];
greekTLower['ή'] = greekTUpper['Ή'] = sLower[7];
greekTLower['ί'] = greekTUpper['Ί'] = sLower[10];
greekTLower['ό'] = greekTUpper['Ό'] = sLower[16];
greekTLower['ύ'] = greekTUpper['Ύ'] = sLower[21];
greekTLower['ώ'] = greekTUpper['Ώ'] = sLower[24];

LTcheck['ά'] = UTcheck['Ά'] = true;
LTcheck['έ'] = UTcheck['Έ'] = true;
LTcheck['ή'] = UTcheck['Ή'] = true;
LTcheck['ί'] = UTcheck['Ί'] = true;
LTcheck['ό'] = UTcheck['Ό'] = true;
LTcheck['ύ'] = UTcheck['Ύ'] = true;
LTcheck['ώ'] = UTcheck['Ώ'] = true;



for (int i=0; i<a.size(); i++){
    if (greekLower[a[i]]==true){
      answer.push_back(a[i]);
    }
    if (greekUpper[a[i]]==true){
        answer.push_back(greekUpper[a[i]]);
    }
    if (TLcheck[a[i]]==true){
        answer.push_back(greekTLower[a[i]]);
    }
    if (UTcheck[a[i]]==true){
        answer.push_back(greekTUpper[a[i]]);
    }
}
return answer;
}

int main(){
system ("chcp 65001");
string test;
cin>>test;
cout<<matchCase(test);
}

However it seems that it does not recognize the Greek letters as valid indexes? perhaps. Any suggestions?