Gtk widget update

have g++\gtk pgm (attached) for linux with a loop that updates a text box. the pgm does not update
the contents of a textbox as expected, and as windows does,. if working properly the pgm should do this:

display in the text box:
"Iteration 001"
then pause 2 seconds

display in the text box:
"Iteration 001"
"Iteration 002"
then pause 2 seconds

..
display in the text box:
"Iteration 001"
"Iteration 002"
...
"Iteration 005"
then pause 2 seconds

just need this dummy pgm fixed so that it displays the updated contents in the text box at the end of each iteration.
want the pgm fixed and running - not suggestions on how to fix it. have blown enough time running down
googled "solutions" that do not work .

thx - j