TOPS-20 User Wiki

User Tools

Site Tools

Trace:
tutorials:basic

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision 		Previous revision
tutorials:basic [2024/10/01 06:38]
papa 		tutorials:basic [2024/10/04 04:14] (current)
papa [Using BASIC]
Line 1: Line 1:
 ====== Using BASIC ====== ====== Using BASIC ======
  
-//[Is an explanation of BASIC needed?]// +TWENEX's BASIC programming system is **LOTS BASIC**, developed at Stanford University. 
-  + 
-TWENEX's BASIC interpreter is **LOTS BASIC**, developed at Stanford University.+Start BASIC with the EXEC command ''BASIC''. Return to EXEC with the BASIC command ''MONITOR''.
  
 The following tutorial is adapted from chapter 17. "Using BASIC" in //LOTS DECSYSTEM-20 Overview Manual//(( The following tutorial is adapted from chapter 17. "Using BASIC" in //LOTS DECSYSTEM-20 Overview Manual//((
Line 121: Line 121:
 |DELETE line number arguments|| |DELETE line number arguments||
 | |Erases the specified lines from core. For example, "DELETE 11,44-212,13" erases line 11, lines 44 through 212, and line 13. If no arguments are specified, an error message is returned. It is not necessary to use the delete command to erase lines. You can erase a line simply by typing its line number and then depressing the return key.| | |Erases the specified lines from core. For example, "DELETE 11,44-212,13" erases line 11, lines 44 through 212, and line 13. If no arguments are specified, an error message is returned. It is not necessary to use the delete command to erase lines. You can erase a line simply by typing its line number and then depressing the return key.|
 +|LIST line number arguments||
 +| |Lists the specified lines of the program currently in core onto the user's terminal. The line number arguments are of the form described under the delete command. If no arguments are specified, the entire program is listed.|
 +|MONITOR|Returns to the EXEC. BASIC may be resumed via CONTINUE. This is just like CTRL/C for most non-BASIC programs. BASIC intercepts CTRL/C aside from returning to BASIC command level.|
 +|NEW dev:filenm.typ||
 +| |The program currently in core is erased from core and the specified filename is established as the name of the "program currently in core". N.B., at the end of execution of this command, no lines exist in core.|
 +|OLD dev:filenm.typ||
 +| |The program currentloy in core is erased from core and the specified file is pulled into core to become the new "program currently in core".|
 +|RENAME dev:filenm.typ||
 +| |Changes the name of the program currently in core to the specified name.|
 +|REPLACE|See SAVE.|
 +|RESEQUENCE|Changes the line numbers of the program currently in core to 10, 20, 30,.... (Line numbers within lines (as, GO TO 1000) are changed appropriately).|
 +|RUN|Compiles and executes the program currently in core. The command RUNNH is equivalent, but runs the program without printing a header.|
 +|SAVE dev:filenm.typ||
 +| |Writes out the program currently in core as a file with the specified name. BASIC will return an error message if save attempts to write over an existing file; to write over a file you must type "REPLACE" instead of "SAVE".|
 +|SCRATCH|Erased from core the program currently in core.|
 +|SYSTEM|Exits from BASIC to monitor level. N.B., the contents of core are lost. You must give the EXEC command REENTER rathre than CONTINUE, START, or BASIC to resume the current BASIC program. "MONITOR" is recommended instead of "SYSTEM".|
 +|UNSAVE dev:filenm.typ||
 +| |Deletes the specified file. More than one file can be specified; for example, UNSAVE DSK:ONE.FOR,SX:TEST.BAS|
  
-====== Original content below ====== +In the commands above which accept such arguments, if "dev:" is omitted, "DSK:" is assumed; if ".typ" is omitted, ".BAS" is assumed. A null file type is indicated by "." with no "typ". The SAVE, REPLACE, and UNSAVE commands allow the "filenm" part of the argument to be omitted, in which case ".typ" must be omitted also and the name and file type of the program currently in core are assumed. 
- +
-You should read a tutorial on using one of the available text editors before reading this tutorial. This tutorial will assume that you're comfortable running programs from the EXEC and creating text files. +
- +
-For a full guide to the BASIC language available, see [[http://manx.classiccmp.org/details/1,18285|the original manual]]. +
- +
-===== Your first BASIC program ===== +
- +
-This section will explain the fundamentals of creating a BASIC program, compiling and running it. +
- +
-BASIC programs require line numbers. You should increment each line by 10 to allow for adding lines in between later. +
- +
-Start by creating a file with the file extension of .B20 with the contents: +
- +
-''10 PRINT "Hello, World!"'' +
- +
-This is the infamous Hello, World! program for the TOPS-20 flavor of BASIC. +
- +
-To run the program, start the BASIC program: +
- +
-''@BASIC'' +
- +
-You will now need to load your program. At the ''READY'' prompt, type: +
- +
-''OLD'' +
- +
-You'll then be prompted for the filename of the source file you created. For instance, if you called the file ''HELLO.B20'' then that's what you should enter. +
- +
-At the next ''READY'' prompt, type ''RUN'' to run the program. You'll see "Hello, World!" printed on the output. +
- +
-In order to build the program for use without the BASIC program, type ''BUILD''. Then return to the EXEC by typing ''MON''. Assuming the program was named ''HELLO.B20'', you should now see a ''HELLO.EXE'' in the same directory. When you run this, you'll see the "Hello, World!" output as before. +
- +
-===== Variables ===== +
- +
-==== Assignment ==== +
- +
- +
-Variable assignment in BASIC is pretty similar to every other programming language. It takes the form of: +
- +
-''VAR = VALUE'' or (optionally) ''LET VAR = VALUE'' +
- +
-Variables do not need to be declared before use. Standard arithmetic operations like +, -, / and * are available for use with either number literals or variable names. +
- +
-==== Types ==== +
- +
-BASIC variable types are determined by an optional suffix to the variable name. A suffix of $ indicates that the variable holds a string. A suffix of % indicates that the variable holds an integer. No suffix indicates that a variable holds a number (possibly with fractional part). +
- +
-It is important to remember that X, X$ and X% are all different variables, not just different interpretations of the same variable. +
-===== Reading Input ===== +
- +
-Reading input from the terminal is rather simple. The function used is called ''INPUT''. +
- +
-The value read can be a number, integer or string depending upon the variable type given as a parameter. +
- +
-The "Hello, World!" program can be extended to be personalised like so: +
- +
-<code> +
-10 PRINT "Enter your name:" +
-20 INPUT X$ +
-30 PRINT "Hello, " + $X + "!" +
-</code> +
- +
-This is also an example of string concatenation. +
-===== Loops ===== +
- +
-Given that every line has a line number, it can become tempting to use the GOTO function. This function gives an unconditional jump to the specified line number. This is a bad idea. +
- +
-"The unbridled use of the go to statement has as an immediate consequence that it becomes terribly hard to find a meaningful set of coordinates in which to describe the process progress. ... The go to statement as it stands is just too primitive, it is too much an invitation to make a mess of one's program." -- Edsger Dijkstra (March 1968). "[[http://dl.acm.org/citation.cfm?doid=362929.362947|Go To Statement Considered Harmful]]". Communications of the ACM 11 (3): 147–148. +
- +
-There are three structured programming loop structures available for use in BASIC: for, while and do. +
- +
-==== for loops ==== +
- +
-==== while loops ==== +
- +
-==== do loops ==== +
- +
-===== Conditionals ===== +
- +
-==== if statements ==== +
- +
-==== switch statements ==== +
- +
- +
-===== Sample Programs ===== +
- +
-//Users should feel free to add their programs to this section.//+
  
-===== See Also =====+The keywords of commands (CATALOG, LIST, etc.) may be abbreviated to their first three letters. Only the three letter abbreviation and the full word form are legal; intermediate abbreviations such as CATAL, for example, are not allowed. If an intermediate abbreviation is used, the extra letters will be seen as part of the command argument (because BASIC does not see blank spaces or tabs at command level.) For example, "CATAL SX:" would be seen as a request to catalog the device "ALSX:". An example of a legal abbreviated command is: CAT DOC:
  
-  * [[tutorials:basic interpreter|Using the BASIC Interpreter]] +Whenever BASIC finishes executing a command, it types "READY". It does not answer "READY" after deleting a line by the alternate method described under the delete command or after receiving a line for the program currently in core from the user's terminal.
-  * [[tutorials:basic advanced|Advanced BASIC Concepts]]+
  
-===== External Resources =====+To insert or replace a line in the program currently in core, simply type the line and then press the RETURN key. BASIC distinguishes between lines (which must be stored or erased) and commands (which must be processed) by the fact that a line always begins with a line number whereas commands all begin with letters. 
  
-  * [[http://bitsavers.org/pdf/dec/pdp10/TOPS20/V4.0_Apr80/AA-H654A-TM_BasicPlus2_Lang_Oct79.pdf|TOPS-20 BASIC-PLUS-2 Language Manual]] 
  
tutorials/basic.1727764686.txt.gz · Last modified: 2024/10/01 06:38 by papa

Page Tools

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki