Combinations without repetition algorithm C++/MFC

This algorithm is written in C++ (with MFC classes), calculates combinations without repetition of characters contained in a string. The algorithm allows to define, during the execution,the length of the string and length combinations, all using a recursive function. For simplicity and to keep the code compact, I used class CStringArray to store the combinations, and class CString to enter the string to process.I also used three global variables needed for the proper functioning of the algorithm. The initialization function is necessary to delete items in CStringArray before a new execution, and define globally the length of the combinations. This function must be called before the function containing the combinatorial algorithm.

CStringArray dani;//global variable
CString temp("");//global variable
int COMBI;//global variable

void inizializzazione(int lungcombinazioni){
COMBI=lungcombinazioni;
dani.RemoveAll();
}

void combinazioni(CString str,int combi){
int tot=str.GetLength();
int rr;
for(int y=0;y<tot;y++){
temp=temp+str[y];
if(temp.GetLength()==COMBI){
dani.Add(temp);
rr=temp.GetLength();
temp=temp.Left(rr-1);
}
else{
if(combi==0)
return;
CString str1;
str1=str.Right(tot-1-y);
combinazioni(str1,combi-1);
rr=temp.GetLength();
temp=temp.Left(rr-1);
}}}