how to use for loop

if i have

[s] = function(data,k)
if (~exist('opts','var'))
 opts = [];
 end
p = 30;
if isfield(opts,'p')
  p = opts.p;
  end
  r = 20;
  if isfield(opts,'r')
  r = opts.r;
  end
  .....
  .....
  [s] = k_means(y,t)

then i take [s] and calculate another function so i want to variables p and r to take range of values i.e p=10:30 and r=5:10 and in each time i have different [s] to complete the calculation