why im getting a sparse error in line 4 in editor, actually my cursor is red

function c = bisection(a,b,tolb)

    while (b-a)/2> tolb

     midp=a+b/2;

   if pb(midp)=0

   fprintf("we found answer")

   break

   end

      if pb(a)*pb(midp)<0

      b=midp;

      else a=midp

      end

end

Answer 1

[Walter Roberson]

You have

     if pb(midp)=0

MATLAB uses == for comparisons, not =