有人能告诉我，最后的while函数为什么会陷入死循环吗？

#include <iostream>
#include <string>
using namespace std;
string a,s;
int cnt = 0,pos;
int main()
{
	getline(cin, a);
	getline(cin , s);
	for (int i = 0; i < a.length(); i++)
	{
		if (a[i]>=65 && a[i] <= 90)
		{
			a[i] += 32;
		}
	}
	for (int i = 0; i < s.length(); i++)
	{
		if (s[i] >=65 && s[i] <= 90)
		{
			s[i] += 32;
		}
	}
	int f = s.find(a,0);
	if (f >= 0)
	{
		cnt++;
		pos = f;
	}
	else
	{
		cout << "-1" << endl;
		return 0;
	}
	int n = f;
	while (pos >=0)
	{
		pos =s.find(a, pos);
		cnt++;
	}
	cout << cnt - 1 << " " << f << endl;
	return 0;
}