Commodore Plus 4 - Page 165

Using the Screen 153
anything else in the line, and then press RETURN. The computer accepts the line
with the new number and retains the old line, too, as long as you remember to
change the line number. If you forget to change the line number, the modified
version of the line will replace the original version.
The program area of memory is not the same as screen memory, so even though
the old line has been overwritten in screen memory, both lines can be intact in
program memory. You can verify that both copies of the line are in program
memory by LISTing the program. For example, type this line and press
RETURN:
10 INPUT^WHAT'SYOURlTAME^jNl
Now cursor back to the line number. Change it to 20, cursor to YOUR NAME
and change it to THE DATE, delete the E from NAME, change N$ to D$, and
press RETURN. The screen should look like this:
20 HTPUT^WHAT'S THE DATE";D$
Line 10 no longer appears on the screen, but it is still in program memory. Issue
a LIST command to display the program, which should look like this:
10 ^
20 INPUT//WHAT/S THE DATE";D$
Remember to press RETURN after you make changes to a line (if you want to
keep the changes, that is). It is a good idea to LIST a program after you make
changes so that you can verify that the changes were made in program memory.
Even experienced programmers sometimes forget to press RETURN.
Quote Mode
When you type a quotation mark, quote mode is turned on and everything you
type is subject to quote-mode rules. Quote mode is turned off when you type a
second quotation mark, when you press the RETURN key, or when you issue an
ESCAPE O sequence.
The following rules define quote mode:
1. The computer does not interpret any characters typed inside quotes, so you can
type anything in quotes without getting a SYNTAX ERROR message when
you execute the command. All non-BASIC characters can and must be
enclosed in quotes except information appearing in REM or DATA statements.
2. Commands do not execute in quote mode.