Why string comparison results an infinite loop - c++

Question

I have a Plane's entity class such as:
class Plane{
private:
string tailNumber;
public:
void setTail(string tail);
string getTail();
}
and a Planes' collection class such as:
class Planes{
public:
void addPlane();
void printDetails();
void printAllPlanes();
private:
vector<Plane> currentPlane;
}
addPlane definition:
void Planes::addPlane(){
Plane a;
string temp;
cout << "Enter tail:";
getline(cin, temp);
a.setTail(temp);
currentPlane.push_back(a);
}
My printDetails definition:
void Planes::printDetails()
{
cout << "Enter Plane's Tail Number: ";
getline(cin, tail);
cin.ignore();
for (unsigned int i = 0; i < currentPlane.size(); i++)
{
if (currentPlane[i].getTailNumber() == tail)
{
//print tail number by calling accessor function}
}
else
{
cout << "Error.";
}
}
and my main class:
int main(){
Plane a;
int userChoice;
do{
cout << "1.Add Plane";
cout << "2.Print All Planes";
cout << "3.Print a plane";
cout << "4.Quit";
cin >> userChoice;
if (userChoice == 1)
a.addPlane();
else if (userChoice == 2)
a.printAllPlanes();
else if (userChoice == 3)
a.printDetails();
}while (userChoice != 4);
return 0;
}
I am successfully adding a new object and print all objects in my vector to display. The problem is if my tail number is: "TGA", then running currentPlane[0].getTail() return "TGA". However, when compare the user-input variable tail = "TGA" with currentPlane[0].getTail() = "TGA" yields an infinite-loop of do-while menu for some reason that I do not understand (because it is a simple string comparison?).
If I only enter integer value such as "12345", then it will jump to the else branch instead of infinite-looping. If I enter any alphanumeric value, then the infinite-looping will appear again.
Can you help me, please?

Answer 1

Nothing to do with string comparisons, the problem with your code is at no point do you set the variable userChoice.
Presumably you meant to have some code somewhere like
cin >> userChoice;
but you don't have anything like that, so the behaviour of your program is undefined.
You really should have had a compiler warning telling you that you are using an uninitialised variable. Pay attention to compiler warnings and fix any that you get.