80-Bus News

D   Characters may be deleted by the use of this command. nD deletes n characters to the right of the cursor where n is an integer in the range 0 to 255 (0 defaults to 1 and if n is omitted, a default of 1 character is assumed). The deleted character(s) are enclosed in backslashes and the cursor will be positioned just to the right of the last character which has been deleted.

S   Searching for a character is carried out by this command which has the general form nSx where n is the nth occurrence of the character ‘x’. The default value for n is 1 and the search begins with the second character to the right of the cursor. All characters passed over by the cursor in its search are printed and if the sought-for character is not found, the cursor will stop at the end of the line; if the search was successful, the cursor will print the character and stop to its right.

K   This has a similar function to the S command but instead of printing all characters as it passes over them, the command deletes them. The command has the general form nKx where n is the nth occurrence of character ‘x’; a default of 1 is assumed.

C   The C command is used for character replacement in a line. It has the general form Cx and changes the character on the right of the cursor to the character ‘x’.

E   The E command terminates editing and outputs a carriage return; unlike the <cr> command, the remainder of the line is not printed.

Q   Typing of Q restores the original line and control is passed to command level.

L   If the L command is used, the remainder of the line is printed , a <cr> is output and then the line number is printed; editing is restarted at the beginning of the line.

NOTE – If, during the running of a program, a SYNTAX ERROR is found, MBASIC will automatically enter the EDIT mode, printing the message ‘Syntax error in nn’, followed by the line number of the offending line. Editing can then start.

The best way to find out how the Editor works is to practice before you write your Pan-galactic Black Hole Simulation program. [Ed. – This is all superfluous if you use the Gemini on screen edit mode or Richards’ SYS, although under these circumstances the line length must not exceed the width of the screen.]

SYSTEM:

The SYSTEM command exits from MBASIC and returns to the disk operating system.

LOAD:

The LOAD command has the format ‘LOAD “<filename>”’ and locates and loads the file into memory ready for use. On completion of a successful load, the ‘Ok’ prompt is given. The first double quote (") is mandatory but the second can be omitted. [Ed. – For drive selection see the note under SAVE.

SAVE:

The SAVE command is used, as its name suggests, to save a program from memory to disk. It has the following format:

SAVE "<filename>",[<disk drive no.>]

The effect of the SAVE command is to leave the current version of the program in the computer’s RAM and to copy an exact replica to disk where it is stored under the <filename>. A frequent cause of program losses is when one inadvertently uses a previously used filename (of a different program) as the <filename>. In this case, the previous program is deleted from disk and replaced with a copy of the current program under the old name – which can be frustrating! The moral is to remember your filenames or to backup your program disks. SAVEing an ASCII file is done by specifying the disk no. (usually 0 or 1), followed by an A – for example, SAVE "TEXT.BAS",0,A saves TEXT.BAS as an ASCII file on drive 0. ASCII files are larger than the normally saved files and are both slower to load and more extravagant of disk space; their chief advantage is that they can be used as direct input to other programs if required.