[newbie] prefered way to enter the values of a matrix interactively

[Jean Dubois]

What is the prefered way to enter the values of a matrix
interactively. I can imagine this is a common task which can be
performed by a predefined matlab-function and it probably is not a
good idea to try to program a function myself for this?
What I want is something like
enter matrix variable name
e.g. a
enter matrix dimension
e.g. 3
enter element 1,1
enter element 1,2
.
.
.enter element 3,3
a=...

thanks in advance