Bryce - how are you creating your GUI? With App Designer, GUIDE, or programmatically? In probably all three cases, your push button will have a callback and it is within that function that you will update the text box with the appropriate value.
If using GUIDE, you could do something like
% pushbutton1 is for the 1 key
function pushbutton1_Callback(hObject, eventdata, handles)
% get the current number from the text field
currentNumber = get(handles.text1, 'String');
% create the new number
newNumber = [currentNumber '1'];
% update the text
set(handles.text1, 'String', newNumber);
The callback uses the handle of the text field (from the handles structure as handles.text1) and gets the current string value. A '1' is then appended to this string and we then save it to the text field.
Your going to have a lot of duplicated code since there will be ten keys, so you may want to create a helper function that does much of the above.
