Problems with constants in prewritten Stochastic indicator

[Stefano Specia]

Hi everybody, unfortunately I didn't manage to find any valuable explanation for a problem.
I'm building a stochastic oscillattor from scratch based on the one built by MT4-5 team and located and named as Stochastic in the 'Indicators' folder.

Supposing they do not possess any value, how can constant variables like rates_total and prev_calculated be inserted in if operators as conditions?
Are these lines crucial for regular functioning of the indicator? Sorry if I don't get the point.
Here is a little part of the code:

int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])

if(rates_total<=InpKPeriod+InpDPeriod+InpSlowing)
      return(0);

pos=InpKPeriod-1;
   if(pos+1<prev_calculated)
      pos=prev_calculated-2;

Thank you in advance!