p=0.2;
n=1;
z=rand(1,1,'uniform');
while( z < 1-p) do z=rand(1,1,'uniform'); n=n+1;end
n

n1=0;
while %t do /// \sleftarrow{\normalfont infinite loop, need a \verb+break+ to quit the \verb+while+}
  z1=rand(1,1,'uniform'); n1= n1+1;
  if ( z1 >= 1-p) then break;end 
end
n1