Help with error running a function

i have the code for #3 of the attached document. For some reason i am getting a warning about the variable p changing size. Im also geting an error for (the code below) which says unrecognized function or variable 'findzero'.

 z = findzero(f,x(k-1),x(k),tol);
 

my code is as follows:

function p = findz(f,a,b,n,tol) 
p = [];
x = linspace(a,b,n+1);

for k = 2:length(x)
    if f(x(k)) * f(x(k-1)) > 0
        continue 
    else
        z = findzero(f,x(k-1),x(k),tol);
        p = [p,z];
    end
end
disp(p)
end