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Programming: BASIC
ZX Spectrum 16K/48K

Chris Bourne


SOME microcomputers, including the Dragon and the BBC microcomputer, have a command call Trace which will run through a program displaying it line by line to show the flow of that program.

The Spectrum has no such command in its Basic language but the omission has been remedied by the release of a machine code routine, also called Trace, for both versions of the computer.

The routine lists a user program line by line; when it reaches a GOTO or GOSUB it will jump to the line specified by that instruction.

If Trace finds an error in a program it will inform the user and if an endless loop has been set up in a user program it will be easier to detect.

Unlike the Trace command on some computers, the routine will allow the program to run while it is executing the Trace. The run is performed in the main part of the screen area and it is useful to compare that output to the program line which is creating it at the bottom of the screen.

The routine provides an effective Trace command and is a useful debugging tool. It is easy to use and can be operated with no knowledge of machine code.

Trace can be obtained from Texgate Computers Ltd, 14 Brook Lane, Corfe Mullen, Dorset, BH21 3RD. The package costs £6.95.

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