How did a vector became a matrix? : So i found this code on the internet but as i'm not that familiar with C++ i found difficult to understand this: how does a vector suddenly becomes a matrix?
thanks! :)

    int main(){
 
    int n;
    string v[MAX];
     
    cin >> n; 
 
    for(int i=0;i<n;i++) 
     cin >> v[i];
  
    for(int i=0;i<n-1;i++){
        int y1,y2;
        y1=v[i].size();
        y2=v[i+1].size();
        for(int j=0; j<y1 && j<y2 ;j++)
            if(v[i][j]!=v[i+1][j]){  // here <-
                int x1,x2;
                x1=(int) v[i][j]-'A';
                x2=(int) v[i+1][j] - 'A';
                m[x1][0]=true; 
                m[x2][0]=true;
                m[x1][x2+1]=true; 
                break;
            }
     }