Author:

• Name: Diomidis Spinellis
  Location: GR - Hellenic Republic (Greece)

To build:

    make all

To use:

    ./dds

Try:

Give the following lines as input:

    OLD LANDER.BAS
    RUN

NOTE: this entry is probably one of the only times CAPS LOCK might be worth having (though still not useful enough to enable :-) ) as all input has to be UPPER CASE.

Judges’ remarks:

Be sure not to run out of fuel!

Author’s remarks:

This is the DDS-BASIC Interpreter (Version 1.00).

Immediate commands:

• RUN
• LIST
• NEW
• OLD filename
• BYE
• SAVE filename

Program commands:

• variable names a to z
• variables initialized to 0 on RUN
• FOR var = exp TO exp
• NEXT variable
• GOSUB exp
• RETURN
• GOTO exp
• IF exp THEN exp
• INPUT variable
• PRINT string
• PRINT exp
• var = exp
• REM any text
• END

Expressions (ranked by precedence):

• Bracketed expressions
• number (leading 0 for octal, 0x for hex, else decimal), variable
• Unary -
• * /
• + -
• = <>
• > <
• <= >=

(* and + are also used for boolean AND and boolean OR)

Boolean expressions evaluate to 0 for false and 1 for true.

Editing:

• Line editor using line re-entry.
• A line number with nothing following it, deletes the line.

Input format:

• Free format positioning of tokens on the line.
• No space is allowed before the line number.
• Exactly one space is needed between the OLD or SAVE command and the filename.
• ALL INPUT MUST BE UPPERCASE.

Limits:

• Line numbers 1-10000
• Line length 999 characters
• FOR nesting 26
• GOSUB 999 levels
• Program Dynamically allocated
• Expressions -32768 - 32767 for 16 bit machines, -2147483648 - 2147483647 for 32 bit machines

Error checking / error reports:

No error checking is performed. It might dump core if a syntax or semantic error is encountered.

Hosting Environment:

ANSI C, traditional K&R C or OSF ANDF ASCII or EBCIDIC character set 48K bytes memory.

The Speed of DDS-BASIC Interpreter (Version 1.00) relative to Microsoft Advanced BASIC 3.31 is approximately 60%.

The code size could be further reduced by doing ugly things like not declaring the return type of functions, not freeing memory, defining define, and joining lines. In its present 1536 character form the program is reasonably portable (it may fail to run in a tagged object architecture) and nicely formatted (it fits in an 80*25 screen).

Primary files

• dds.c - entry source code
• Makefile - entry Makefile
• dds.orig.c - original source code
• LANDER.BAS - BASIC source code for Lunar Lander game

Secondary files

• 1990_dds.tar.bz2 - download entry tarball
• README.md - markdown source for this web page
• .entry.json - entry summary and manifest in JSON
• .gitignore - list of files that should not be committed under git
• .path - directory path from top level directory
• index.html - this web page

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