Also, if you find the need to add a line in the middle, after entering the program, you should be able to just use a line number that falls in between the line numbers already in use. For example, if your existing code is:
100 CALL CLEAR :: CALL SCREEN(2)
105 X$="HELLO, WORLD!" :: R=10 :: C=11 :: X=LEN(X$)
110 FOR P=1 TO X :: P$=SEG$(X$,P,1):: CALL HCHAR(R,C,ASC(P$)):: C=C+1 :: NEXT P
115 GOTO 115
Now you type RUN and hit the "Enter" key... The screen turns black, and... WTF?!? Nothing! You facepalm and realize that you forgot to change the screen color after all the text is printed. No problem! You FCTN-4, type
112 CALL SCREEN(14)
and RUN again.
If your line numbers are incremented by 1 and you need to add a line, you can RESEQUENCE your line numbers. just type
RES 10,5
and your program will now start at line 10, with line numbers incremented by 5. All GOTO and GOSUB statements will automatically be updated with the correct new line numbers. The only thing is, if any statement references a line number that doesn't exist, the invalid number is changed to 32767.