Recursive function and apvector

I have the task of creating a program that lets the user input numbers into an apvector then let them enter a goal(final number), and have a recursive function tell whether or not the numbers in the apvector can add up to be exactly the goal number. Im not sure where to start but this is what i have done so far.

Code:

`bool IsPossible(const apvector <int> &A, int goal)`

{

// I think i need code to add the elements of an apvector but

//I dont know how to do something like that

if( ***** == goal)

return true;

else

}