Commodore CBM - Programmed Cursor Movement; The PRINT Statement

ln the example above. note that line 50 does not check for negatlve num-
bers. If both numbers are negative, then the leading character of T$ should not
be
dropped: this allows the negative sign to appear in front of the entire number W$.
If the
two strings have different signs, they should not be concatenated. When
concatenating two strings with different signs, the following answers result:
T$ 1 tbl1l21314151 + Q$ 1-16171s19101 = W$ .1121314151116171s19101 Incorrect
T$
[-11121314151 + Q$ 1 ~16171s191ol = W$ BlfITd112131411516171s19101 Incorrect
ln summary, any type of string can be concatenated. The only string
type that must be treated differently
is a numeric string converted from a
non-string source.
When the extra space for the sign of numeric strings is taken
into consideration. then string concatenation becomes
an easy, useful tool.
PROGRAMMED CURSOR MOVEMENT
ln Chapter 2 we discussed the screen editing capabilities of six PET cursor
control keys: CLEAR SCREEN/HOME, CURSOR UP/DOWN, CURSOR
LEFT /RIGHT. INSERT /DELETE, RETURN, and REVERSE.
Although these six cursor keys function in immediate mode. it is also possi-
ble to program cursor movement. This allows vou to move
output on and around
the screen du ring program execution, when manual cursor movement via the
keyboard
is inhibited. By programming cursor movement vou can format output
without using programmed spaces and end-oHine checks.
Vou can program cursor movement using 1) the PRINT statement, and
2) the CHR$ function.
This section will concentrate on programming cursor
movement
with the PRINT statement. Cursor movement using the CHR$ function
will be discussed in the following section, "Programming Characters in ASCII."
THE PRINT STATEMENT
Only four of the six cursor keys are programmable using the PRINT
statement:
CLEAR SCREEN/HOME, CURSOR UP/DOWN. CURSOR LEFT/RIGHT,
and
REVERSE. The INSERT/DELETE key and the RETURN key are not pro-
grammable
with the PRINT statement.
The programming rules to print any character apply also to cursor move-
ment
keys. The first step is to type PRINT followed by a set of quotation marks:
PRINT'"
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