To define the term Stateless and stateful just  check out the give program.

STATELESS
//The state is derived by what is passed into the function

function int addOne(int number)
{
    return number + 1;
}

Stateful

//The state is maintained by the function

private int _number = 0; //initially zero 

function int addOne()
{
    _number++;
    return _number;
}