GWBASIC User's Manual

GW-BASIC User's Guide
together in a logical manner to create programs. The GW-BASIC User's Reference describes all of
the statements available for use in GW-BASIC.
In a GW-BASIC program, lines have the following format:
nnnnn statement[statements]
nnnnn is a line number
statement is a GW-BASIC statement.
A GW-BASIC program line always begins with a line number and must contain at least one
character, but no more than 255 characters. Line numbers indicate the order in which the program
lines are stored in memory, and are also used as references when branching and editing. The
program line ends when you press the RETURN key.
Depending on the logic of your program, there may be more than one statement on a line. If so,
each must be separated by a colon (:). Each of the lines in a program should be preceded by a
line number. This number may be any whole integer from 0 to 65529. It is customary to use line
numbers such as 10, 20, 30, and 40, in order to leave room for any additional lines that you may
wish to include later. Since the computer will run the statements in numerical order, additional
lines needn't appear in consecutive order on the screen: for example, if you entered line 35 after
line 60, the computer would still run line 35 after line 30 and before line 40. This technique may
save your reentering an entire program in order to include one line that you have forgotten.
The width of your screen is 80 characters. If your statement exceeds this width, the cursor will
wrap to the next screen line automatically. Only when you press the RETURN key will the
computer acknowledge the end of the line. Resist the temptation to press RETURN as you approach
the edge of the screen (or beyond). The computer will automatically wrap the line for you. You
can also press CTRL-RETURN, which causes the cursor to move to the beginning of the next screen
line without actually entering the line. When you press RETURN, the entire logical line is passed to
GW-BASIC for storage in the program.
In GW-BASIC, any line of text that begins with a numeric character is considered a program line
and is processed in one of three ways after the RETURN key is pressed:
● A new line is added to the program. This occurs if the line number is legal (within the
range of 0 through 65529), and if at least one alpha or special character follows the line
number in the line.
● An existing line is modified. This occurs if the line number matches the line number of an
existing line in the program. The existing line is replaced with the text of the newlyentered
line. This process is called editing.
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