editbox

Hi,
Someone Know any command to read a string form the editbox??
I want to introduce in the editbox a function, for example sin or
cos, I want the editbox read the string and analyze it for using this
function to fill a matrix.
I think the "eval" command maybe correct, but I do not know to use
it.

Thank you and sorry my poor english.

Víctor Pizarro Sánchez