i+1 index of int's vector

[bioit]

Hello I've big problem with my vector... I'd like to get the value from it, but not i index but i+1 index. Compilator shows this:
'lvalue required as left operand of assignment'

My vector has 4 int fields and need to change those values during the algorithm work. Here's my code. I signed trouble lines by '/////'.
Could somebody show me how to resolve this issue? I've read that Get and Set methods can be usefull but I don't know how to implement them... I'll be veeeery glad that somebody fix M1[j+1].Time() that it'll returns needed value.

#include <iostream>
#include <string>
#include <vector>
#include <fstream>
#include <cstddef>
#include <cstdlib>
#include <iterator>
#include <algorithm>
using namespace std;
class Item
  {
   public:
   int time, dist, index, deadline;
   Item(int time=0, int dist=0, int index=0, int deadline=0):time(time),dist(dist), index(index), deadline(deadline) {}
   int Time()const { return time; } //a
   int Dist()const { return dist; } //b
   int Index()const { return index; } //c
   int Deadline()const { return deadline; } //d
  };
  void permutation(int k, int n, vector<Item> M1, vector<Item> M1_wh)
{
    int result=0, diff = 0;
    if(k==0)
        {
            int g=0, j=0;
            for(int i=0; i<n; i++)
            {
                for(j=j+g; j<n; j++)
                {
                    if(M1_wh[i].Dist()==M1[j].Dist())
                    {
                        if(M1_wh[i].Index()==0)
                        {
                        result = M1_wh[i].Time() + M1[j].Time();
                        M1[j+1].Time() = M1[j+1].Time() + result;// here it starts, every place where it's j+1 or i+1 :((
                        g++;
                        }
                        else
                        {
                        result = M1[j].Time();
                        M1[j+1].Time() = M1[j+1].Time() + result;
                        g++;
                        }
                    }
                    if(M1_wh[i].Dist()>M1[j].Dist())
                    {
                        if(M1_wh[i].Index()==0)
                            {
                            result = M1_wh[i].Time() + M1[j].Time();
                            M1[j+1].Time() = M1[j+1].Time() + result;
                            M1_wh[i].Dist() = M1_wh[i].Dist() - M1[j].Dist();
                            g++;
                            }
                        else
                            {
                            result = M1[j].Time();
                            M1[j+1].Time() = M1[j+1].Time() + result;
                            M1_wh[i].Dist() = M1_wh[i].Dist() - M1[j].Dist();
                            g++;
                        }
                        for(int t=j+1; t<n; t++)
                        {
                            if(M1_wh[i].Dist()>M1[t].Dist())
                            {
                            result = M1[t].Time() + M1[t+1].Time();
                            M1[t+1].Time() = result;
                            M1_wh[i].Dist() = M1_wh[i].Dist() - M1[j].Dist();
                            g++;
                            }
                            else
                            {
                                t=n;
                            }
                        }
                    }
                    if(M1_wh[i].Dist()<M1[j].Dist())
                    {
                        if(M1_wh[i].Dist() > 0)
                        {
                        if(i==0 && j==0)
                        {
                            result = M1_wh[i].Time() + M1[j].Time() + M1_wh[i+1].Time();
                            M1[j+1].Time() = M1[j+1].Time() + result;
                            diff = M1[j].Dist() - M1_wh[i].Dist();
                            M1_wh[i+1].Dist() = M1_wh[i+1].Dist() - diff;
                            M1_wh[i+1].Index() = 1; 
                            g++;
                        }
                        else
                        {
                            result = M1[j].Time() + M1_wh[i+1].Time();
                            M1[j+1].Time() = M1[j+1].Time() + result;
                            diff = M1[j].Dist() - M1_wh[i].Dist();
                            M1_wh[i+1].Dist() = M1_wh[i+1].Dist() - diff;
                            M1_wh[i+1].Index() = 1;
                            g++;
                        }

                    }
                    }
                }
            }

        }
    /*
    for(int i=0; i<n; i++)
    {
        cout << M1[i].Time() << " " <<M1[i].Dist() <<" "<< M1[i].Index() << " " << M1[i].Deadline() << endl;
    }
            cout << endl;
            */

else{
        for(int i=0; i<k+1; i++)
        {
              Item tmp = M1[i];
              M1[i] = M1[k];
              M1[k] = tmp;
              permutation(k-1, n, M1, M1_wh); 
              tmp = M1[i]; 
              M1[i] = M1[k];
              M1[k] = tmp;
        }
        }
}
int main()
{
    vector<Item> M1; 
    vector<Item> M1_wh; 
    vector<Item> M2; 
    int a=0,b=0,c=0,d=0,n=0, k=0;
    int x=0,y=0,z=0,v=0, T=0;
    //Item result;
    //Item diff;
    ifstream filee;
    filee.open("tasks.txt", ios::in);
    filee>>n;
    k = n-1;
    for(int i=0; i<n; i++)
    {
        filee >> a >> b >> c >> d;
        M1.push_back(Item(a,b,c,d));
    }
    filee.close();
    cout << " " << endl;
    cin >> x;
    cout << " " << endl;
    cin >> T;
   for(int i=0; i<n; i++)
   {
       z,v=0;
       y = rand() % T + 1;
       M1_wh.push_back(Item(x,y,z,v));
   }

permutation(k, n, M1, M1_wh);
return 0;
}

[MiiNiPaa]

Time() etc. methods returns temporary copy of internal value which cannot be assigned to. Either return by reference or assign to internal variables directly.

[bioit]

M1[i+1].time instead of M1[i+1].Time()
solved ;>