I am trying to increment a variable in a loop as shown below:

Set V[serv_num] "50000000"

Set V[line_num] "5"

label start_loop

Set various fields........

...................

...................

Set V[serv_num] &[serv_num] + 1

Set V[line_num] &[line_num] + 1

goto start_loop

The variable line_num increments OK but serv_num does not. If I reduce it to 7 digits or less it is OK. Is there a limit to the size of a variable?

Yes; the reason for the limit is that we use "float" variables for the calculations; they allow only 7 significant digits. We have now changed this (version GuiXT 2001 Q3 08) to type "double", allowing up to 15 digits.