Line labels are the preferred method of identifying lines in Basic. Line Labels are used to identify the target of a Goto or a Gosub.
A line label is a unique name that appears on a line by itself and ends with a colon.
For Example:
a = 0
Main:
CLS
Print a
Gosub Calc
Wait 500
If a < 100 Then Main
End
Calc:
a = a + 1
Return