C++ Graeffe's square root method

[klika]

So i have to write a c++ program for the Graeffe's square root method
I have am stuck here when i have this formula transform into c++ code

The code works particulary, the bolded part doesn't, it's beeing ignored and i don't know why... can any one help me?


http://latex.codecogs.com/gif.latex?A_{k}=a_{k}^{2}+2\sum_{s=1}^{k}(-1)^{s}a_{k-s}*a_{k+s},&space;k=0,....n

 	cout<<"How many elements?"<<endl;
	cin>>n;
	cout<<"Insert the elements:"<<endl;
	for(int i=0; i<n; i++)
	{
		cin>>elem[i];
		
	}
	
	
	C[0]=pow(elem[0],2);
	
	for(int j=1; j<n; j++)
	{
		C[j]=pow(elem[j],2);
	
			int i=1;
			while((i+j)<=n-1&&(i<=j))
			{
				
				C[j]=C[j]+(-1)^i*2*(elem[j-1]*elem[j+i]);
				i=i+1;
			
			}
	

			cout<<"C"<<j<<":"<<C[j]<<endl;
	
	}