stop in foo {print a; where} after 10
stops execution the tenth time in the function foo, prints a, and executes the where command.
stop at "bar":17 if a == 0
stops execution at line 17 of file bar if a is equal to 0.
stop a
stops execution whenever the value of a changes.
stop if a .eq. 5 after 3
stops execution the third time a equals 5.