Incompatible Vector Iterators?

Question

I was solving a programming problem that involved a set of all p^2 + q^2 such that p and q are less than M. In order to solve the problem, I decided to create a sorted vector. However, the following code doesn't seem to work. It seems to be giving an incompatible vector iterators error at the

if (iter == bisquares.end()) {

The code is given below.

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    ifstream fin("ariprog.in");
    ofstream fout("ariprog.out");

    int N, M;
    fin >> N >> M;

    vector<int> bisquares;
    bisquares.push_back(0);

    for (int i = 0; i <= M; i++) {
        for (int j = 0; j <= M; j++) {
            int bisquare = i * i + j * j; 
            vector<int>::iterator iter = bisquares.begin();
            while (iter != bisquares.end()) {
                if (bisquare < *iter) {
                    iter++;
                    bisquares.insert(iter, bisquare);
                    break;
                }
                if (bisquare == *iter) {
                    break;
                }
                iter++;
            }
            if (iter == bisquares.end()) {
                bisquares.push_back(bisquare);
            }
        }
    }

    // Print Elements
    for (int i = 0; i < bisquares.size(); i++) {
        cout << bisquares[i] << " ";
        if (i % 10 == 9) {
            cout << endl;
        }
    }

    fin.close();
    fout.close();

    return 0;
}

The file ariprog.in contains

3
5

I'm not exactly sure what's going on. Any help is appreciated.