tutorials:basic
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tutorials:basic [2013/07/14 17:12] irl [Loops] |
tutorials:basic [2024/10/04 04:14] (current) papa [Using BASIC] |
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| - | ====== **Under Construction** ====== | ||
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| - | This page is under construction by user IRL. Please don't mess with it until I've removed this message. I'll be working on this over the next few hours. | ||
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| - | --- // | ||
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| ====== Using BASIC ====== | ====== Using BASIC ====== | ||
| - | 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. | + | TWENEX's BASIC programming system is **LOTS |
| - | + | ||
| - | For a full guide to the BASIC language available, see [[http:// | + | |
| - | + | ||
| - | ===== 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: | + | |
| - | '' | + | Start BASIC with the EXEC command |
| - | This is the infamous Hello, World! program for the TOPS-20 flavor of BASIC. | + | The following tutorial |
| + | //LOTS DECSYSTEM-20 Overview Manual//. (1984). Accessed: October 1, 2024. [Online]. Available: | ||
| + | http:// | ||
| - | To run the program, start the BASIC program: | + | (Although not strictly relevant to LOTS BASIC, a description of the BASIC programming language largely the same as that supported by LOTS BASIC can be found in // |
| + | ===== BASIC Example ===== | ||
| - | '' | + | For those already familiar with BASIC and who would like a summary of LOTS BASIC commands, skip the following example and see [[#BASIC Command Summary|BASIC Command Summary]]. |
| - | You will now need to load your program. | + | Here is an example of how you might start BASIC, enter a program |
| - | '' | ||
| - | You'll then be prompted for the filename of the source file you created. | + | > '' |
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| - | At the next '' | + | BASIC types a greeting message, spaces down a line and stops. We may no begin typing in our program, including |
| - | In order to build the program for use without the BASIC program, type '' | + | > '' |
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > ''__50 print "The square of",a,"is", | ||
| + | > '' | ||
| + | > '' | ||
| - | ===== Variables ===== | + | We have finished typing in the program, so we ask BASIC to run it by typing the RUN command. BASIC knows this command is not part of the program because it does not begin with a line number. BASIC types out the name of the program and the date and time. The heading " |
| - | ==== Assignment ==== | + | > '' |
| + | > '' | ||
| + | > ''? | ||
| + | > '' | ||
| + | > | ||
| + | > '' | ||
| + | BASIC tells us that the program needs an END statement, then it tells us how long the run took. When BASIC types READY, it means that it is waiting for another command or a new program line. We need to add an END statement, which is always the last line in a program. We can give it any number greater than 70. The line numbers aren't required to be incremented by tens. | ||
| - | Variable assignment in BASIC is pretty similar to every other programming language. It takes the form of: | + | > '' |
| - | '' | + | Now our program should run, so we try it again. The "?" |
| - | Variables do not need to be declared before use. Standard arithmetic operations like +, -, / and * are available for use with either | + | > '' |
| + | > | ||
| + | > '' | ||
| + | > | ||
| + | > '' | ||
| + | > ''? | ||
| + | > '' | ||
| + | > '' | ||
| + | > ''? | ||
| + | > '' | ||
| + | > '' | ||
| + | > ''? | ||
| + | > '' | ||
| + | > | ||
| + | > '' | ||
| - | ==== Types ==== | + | By the way, you probably understood the program as it was written, without any commentary on our part; this illustrates the advantage of BASIC: it is easy to understand. Now let's add one more line. |
| - | BASIC variable types are determined by an optional suffix to the variable name. A suffix of $ indicates | + | > '' |
| - | It is important | + | It makes perfect sense to insert this line between lines 50 and 60, and this is what BASIC does. Let's see what the program looks like now. The " |
| - | ===== Reading Input ===== | + | |
| - | Reading input from the terminal is rather simple. | + | > '' |
| + | > | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > | ||
| + | > '' | ||
| - | The value read can be a number, integer or string depending upon the variable type given as a parameter. | + | We rerun the program to see the effect of the new line. |
| - | The " | + | > '' |
| + | > | ||
| + | > '' | ||
| + | > ''? | ||
| + | > '' | ||
| + | > '' | ||
| + | > '' | ||
| + | > ''? | ||
| + | > '' | ||
| + | > | ||
| + | > '' | ||
| - | < | + | Having put so much effort into our program, we would like to keep it around for later use. In saving it, we decide to give it the name TEST. |
| - | 10 PRINT "Enter your name:" | + | |
| - | 20 INPUT X$ | + | |
| - | 30 PRINT "Hello, " + $X + " | + | |
| - | </ | + | |
| - | This is also an example of string concatenation. | + | > '' |
| - | ===== Loops ===== | + | > |
| + | > '' | ||
| - | Given that every line has a line number, it can become tempting | + | In the future, when we are in BASIC and want to retrieve this program, we would use the command "OLD TEST". We have reached the end of our example, se we return |
| - | "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." | + | > '' |
| + | > '' | ||
| - | There are three structured programming loop structures available for use in BASIC: for, while and do. | + | We will find our saved program on our disk area under the name TEST.BAS. |
| - | ==== for loops ==== | + | ===== BASIC Command Summary ===== |
| - | ==== while loops ==== | + | This is a summary of commands in version 17D of LOTS BASIC. |
| - | ==== do loops ==== | + | |CTRL/ |
| + | |BYE|Logs you completely off the system.| | ||
| + | |CATALOG dev:|Lists onto the user's terminal the names of the user's files which exist on the specified device.| | ||
| + | |COPY dev: | ||
| + | | |Copies the first file onto the second.| | ||
| + | |DELETE line number arguments|| | ||
| + | | |Erases the specified lines from core. For example, " | ||
| + | |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: | ||
| + | | |The program currently in core is erased from core and the specified filename is established as the name of the " | ||
| + | |OLD dev: | ||
| + | | |The program currentloy in core is erased from core and the specified file is pulled into core to become the new " | ||
| + | |RENAME dev: | ||
| + | | |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: | ||
| + | | |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 " | ||
| + | |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. " | ||
| + | |UNSAVE dev: | ||
| + | | |Deletes the specified file. More than one file can be specified; for example, UNSAVE DSK: | ||
| - | ===== Conditionals ===== | + | In the commands above which accept such arguments, if " |
| - | ===== Sample Programs ===== | + | 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 " |
| - | //Users should feel free to add their programs to this section.// | + | Whenever BASIC finishes executing a command, it types " |
| - | ===== 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:// | ||
tutorials/basic.1373821922.txt.gz · Last modified: 2013/07/14 17:12 by irl
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