Solution
The Module command can be used to wrap a set of commands into a single function. The first argument is the declaration of any possible local variables.
In[55]:=
Out[57]=
![nmax = 100 ; Clear[x, y, f, n, z, n0]](../HTMLFiles/ex08_solutions_113.gif){kind=small}
![f[x_, y_] := Module[{n}, n = 0 ; For[z0 = 0 ; z = 0, Norm[z] <2&&n<nmax, z0 = z, z = z0^2 + x + I y ; n ++] ; Return[n]] ;](../HTMLFiles/ex08_solutions_114.gif)
![Plot3D[f[x, y], {x, -2, 1}, {y, -1, 1}, PlotPoints100]](../HTMLFiles/ex08_solutions_115.gif){kind=small}
![[Graphics:../HTMLFiles/ex08_solutions_116.gif]](../HTMLFiles/ex08_solutions_116.gif)
