BFS Implementation in cpp

Program:-

#include <bits/stdc++.h>
using namespace std;

int main() {
    int n,m;
    cin>>n>>m;
    vector<int>vec[n];
    for(int i=0;i<m;i++){
        int a,b;
        cin>>a>>b;
        a--;b--;
        vec[a].push_back(b);
        vec[b].push_back(a);
    }
    vector<int>dist(n,-1);
    dist[0]=0;//starting number is always 0..
    queue<int>que;
    que.push(0);
    while(!que.empty()){
        int index=que.front();que.pop();
        for(int i=0;i<vec[index].size();i++){
            if(dist[vec[index][i]]==-1){
                dist[vec[index][i]]=dist[index]+1;
                que.push(vec[index][i]);
            }
            /*if(dist[vec[index][i]]==dist[index]) {
                cout<<"Biparite Graph\n";
                return 0;
            }*/
        }
    }
    cout<<"Distance from starting vertex\n";
    for(int i=0;i<n;i++) cout<<dist[i]<<" ";
    return 0;
}