General :: Interface Not Responding In Glade 3 / Gtk With C

I am a fairly new ubuntu user. I am using ubuntu 10.04 and glade 3 for building a simple interface that uses C. In my interface , I have created two buttons : start and stop .Tofocus on my actual problem , I have created a simpler UI and code. start button runs a while(1) loop and stop should stop the loop .

The problem is , when I press start , the gui freezes and I cannot press any other button. I cant even close my app.After some thorough experimentation, I found out that when I press start, it never comes out of the while loop. I need the loop to keep running until I press stop . What should i do? Here are the functions for the clickable buttons :

Code:
void
on_start_button_clicked (GtkButton *button, gpointer user_data)
{
flag1=0;
while(1)
{
printf("**********checking !!!! ********
[Code]....