Band Reject Filter Design

I want to design a band reject filter to stop certain frequencies from a Sinc function, i used heaviside function to create the band reject filter then i multiplied the filter by the Sinc function and it worked(code below) my question is: Is using this filter is okay or it can cause invisible errors?

if true
Fstart = 'Please Enter start frequency: ';
Fst=input(Fstart);
Fend='please Enter End frequency: ';
Fen=input(Fend);
BR=(1-((heaviside(f-Fst)-heaviside(f-Fen))+(heaviside(-f-Fst)-heaviside(-f-Fen))));
filter=BR.*Signal;
end