In my experience, the best way to learn programming is to write some code, run it and see what happens. If you are successful, the next step is to change some parameters and re-run. Of course you need to know the basic rules.
Scilab is one of the programs I have been using for my work for last one and half years. I have found it quite useful and easy to learn. It is free-clone of Matlab. It have a lot of useful tools. Let us see what the following program does. If you find interesting I will explain about the codes in detail in my next postings.
[note: before using the program you will need to download scilab from www.scilab.org]

mode(-1)
for k=1:1
if k<10 then
kk='0'+string(k)
else
kk=string(k)
end

clf
// rect=[-k,-k,k,k];
// tics=[1,2,1,2];
// plotframe(rect,tics)
drawlater
f=gcf()
f.figure_size=[500,500]
for theta=10:10:180
j=0
t=theta*%pi/180
for i=-3:0.1:3
j=j+1
y(j)=i
x(j)=(1-y(j)^2/9)
x(j)=x(j)^0.5*5
end
for i=3:-0.1:-3
j=j+1
y(j)=i
x(j)=(1-y(j)^2/9)
x(j)=x(j)^0.5*5
x(j)=-x(j)
end
xnew=[x,y]*[cos(t),sin(t);sin(t),-cos(t)]
x1=xnew(:,2)
y1=xnew(:,1)
plot(x1,y1,'-r')
end
a=gca()
a.isoview="on"
a.axes_visible = ["off","off","off"]
drawnow
// xs2gif(0,'c:/TEMP/'+kk+'.gif')
end

Yes you are right Scilab is nice little program to learn numerical programming. One can easily switch to Matlab after learning this program.
If any body is interested in similar program for symbolic and also for some numerical programming just like in Maple and in Mathematica check out Maxima. It is also a free program. Click below for more

- http://maxima.sourceforge.net/

how fast is it's compiler/interpreter? any advantage over matlab?

My intention was to attract novices to programming. For those who are already using high-level-programming like MATLAB, I have nothing much to say.
I have used both SCILAB and Matlab for simple engineering problems. I have not found much difference in the speed. The biggest difference between Scilab and Matlab is the price. In my case Scilab has been sufficient to solve my problem.
I am putting one for gif file.

Thank u akawi for information.It's really useful for me.