The detailed discussion of the problem is shown in [this link](https://stackoverflow.com/questions/45990714/how-to-print-the-values-of-two-dimensional-pair-vector/45991023#45991023). I am trying to sum up two instance variable defined inside class `Point` and assign it to a different variable `temp`. 

```
class Point{
    public:
      double x;  
      double y;       
      friend istream& operator>>(istream& input, Point& p);
      double operator=(Point& p);      
      double getSqX(void);      
      double getSqY(void);
      double LengthSquared(void);  

    };    
      double Point::getSqX(void){
          return pow(x,2);}

      double Point::getSqY(void){
          return pow(y,2);}

       double Point::LengthSquared(){ return getSqX() + getSqY(); }

    istream& operator>>(istream& input, Point& p){
     ... // over load the >> operator      
      return input;
    };

     int main(){
        double temp;        
        vector<vector<Point> > FFTfile= some function that loads data();        
        for (int i = 0; i < FFTfile.size(); i++){
            for (int j = 0; j < FFTfile[i].size(); j++){
                 temp=FFTfile[j].LengthSquared();            
            }           

        }       
        return(0);
}

```

Edit:  

Based on the suggestions, I created a method LengthSquared(), but I still get following error: 

```
 error: 'class std::vector<Point>' has no member named 'LengthSquared'  temp=FFTfile[j].LengthSquared();

```