How do I implement a while loop to this function - c++

Question

I am working on a school project where we will make a contact book. In one of the functions, it must find contacts using the first name.
The error that occurs is that it only shows one contact in the vector. I want all contacts with the same name to be displayed.
How do I implement a loop or counter (i++) so that it includes all contacts with the same name and not just take the first index?
Im new to C++ and appreciate all help :)
My function:
int findTargetFirstName(vector<Kontaktbok>& bok, string target) {
for (int i = 0; i < bok.size(); i++)
if (bok[i].fnamn == target) return i;
return -1;
void search(vector<Kontaktbok>& bok) {
if (bok.size() > 0) {
string firstname;
cout << "First name of the contact: ";
getline(cin, firstname);
int pos = findTargetFirstName(bok, firstname);
cout << "Firstname, Lastname, Address, Pnummer, E-post, Telefonnummer" << endl;
if (pos>=0) {
cout << left;
cout << setw(10) << bok[pos].fnamn << left
<< setw(15) << bok[pos].enamn << left
<< setw(20) << bok[pos].adress << left
<< setw(15) << bok[pos].pnummer <<left
<< setw(25) << bok[pos].epost <<left
<< setw(15) << bok[pos].telnummer << left << endl;
}
cout << "********************************************************************************" << endl;
}
}

Answer 1

One way is adding a parameter to determine which element to start from.
int findTargetFirstName(vector<Kontaktbok>& bok, string target, int start = 0) {
for (int i = start; i < bok.size(); i++)
if (bok[i].fnamn == target) return i;
return -1;
}
void search(vector<Kontaktbok>& bok) {
if(bok.size() > 0) {
string firstname;
cout << "First name of the contact: ";
getline(cin, firstname);
int pos = findTargetFirstName(bok, firstname);
cout << "Firstname, Lastname, Address, Pnummer, E-post, Telefonnummer" << endl;
while (pos>=0){ // change if to while
cout << left;
cout << setw(10) << bok[pos].fnamn << left
<< setw(15) << bok[pos].enamn << left
<< setw(20) << bok[pos].adress << left
<< setw(15) << bok[pos].pnummer <<left
<< setw(25) << bok[pos].epost <<left
<< setw(15) << bok[pos].telnummer << left << endl;
pos = findTargetFirstName(bok, firstname, pos + 1); // search for next contact
}
cout << "********************************************************************************" << endl;
}
}
Another way is having the function findTargetFirstName return a vector of contacts that meets the condition.
vector<int> findTargetFirstName(vector<Kontaktbok>& bok, string target) {
vector<int> ret;
for (int i = start; i < bok.size(); i++)
if (bok[i].fnamn == target) ret.push_back(i);
return ret;
}
void search(vector<Kontaktbok>& bok) {
if(bok.size() > 0) {
string firstname;
cout << "First name of the contact: ";
getline(cin, firstname);
vector<int> poses = findTargetFirstName(bok, firstname); // change type and variable
cout << "Firstname, Lastname, Address, Pnummer, E-post, Telefonnummer" << endl;
for (int pos : poses){ // change if to range-based for
cout << left;
cout << setw(10) << bok[pos].fnamn << left
<< setw(15) << bok[pos].enamn << left
<< setw(20) << bok[pos].adress << left
<< setw(15) << bok[pos].pnummer <<left
<< setw(25) << bok[pos].epost <<left
<< setw(15) << bok[pos].telnummer << left << endl;
}
cout << "********************************************************************************" << endl;
}
}