What can cause this program failure showing floating point exception?

I'm not able to find the error in this code below sometimes it showing floating-point exception and sometimes it prints the output showing time limit exceed.

      #include<bits/stdc++.h>
      using namespace std;
       int main(){long int t,i,j,n,k,start,d,z;
      long int pos;


      cin>>t;
        for(i=0;i<t;i++){
               cin>>n>>k;

            vector<int>myset(n+1);
          vector<int>::iterator it; 


           for(j=0;j<n;j++) {
               z=j+1;
             myset.push_back(z);
              }
          it=myset.begin();
           pos=0;
           int m=n;
           start=2;


             while(k>0){
               start=(start+2);
             if(start>m){
              start=start%m;
           }
              k=k-1;
           }

         it=myset.begin();
             pos=start-1;
          it=it+pos;
            myset.erase(it);

          d=start;


         while(!myset.empty()){
            it=myset.begin();
             pos=((pos+2)%m);
             start=myset[pos];

              it=it+pos;
           myset.erase(it);
             m=m-1;
             pos=pos-1;
              d=start;
               }
           cout<<d<<"\n" ;
            }
             }



     What is the error in this code?
     I'm not able to find the actual error in this code but most probably I think the error in this vector declaration but not sure help me to find out the error in this code?

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