Editing BASIC Programming (section)

==Details==
[[Image:Basicprogramming.png|thumb|upright=2|Main display]]

The ''BASIC Programming'' display is divided into six regions:

* '''Program''' is where instructions are typed. It has a maximum of eleven lines of code.
* '''[[Call stack|Stack]]''' shows temporary results of what the program does. 
* '''[[Variable (computer science)|Variables]]''' stores the values of any variables that the program is using. 
* '''Output''' displays any output values that the program creates. 
* '''Status''' shows the amount of available memory remaining.
* '''Graphics''' contains two colored squares that can be manipulated by the program.

Input is given through two Atari keypad controllers, which came with special overlays to show how to type the different commands and letters.<ref>[https://atariage.com/controller_page.html?ControllerID=4&SystemID=2600 Controllers - Atari Keypad], {{Webarchive|url=https://web.archive.org/web/20150615042830/https://atariage.com/controller_page.html?ControllerID=4&SystemID=2600 |date=15 June 2015 }} Atari KeypadSystem: Atari 2600, Model Number: CX50, ''Sold in pairs, functionally identical to the Kid's Controller and the Video Touch Pad. Included overlays with commands, meant to be used with Basic Programming.''</ref>  Programs are restricted to 64 characters in size and normally 9 lines of code, limiting the programs that can be written (users can disable all windows except Program and keep selecting "New Line" until 11 lines of code are present).

===Language features===

VCS BASIC supports the following keywords:<ref>{{cite book|title=BASIC Programming: Atari Game Program Instructions|date=1979|publisher=Atari, Inc.|location=Sunnyvale, CA}}</ref>
* Statements: <code>Print</code>
* Structure: <code>Goto</code>, <code>If-Then-Else</code>
* Graphics: <code>Clear</code>
* Functions: <code>Hit</code>, <code>Key</code>
* Math: <code>+ - × ÷ Mod</code>
* Relational operators: <code>< > =</code>

Unlike most BASIC implementations of the time:
* VCS BASIC uses ← instead of = for assignment; e.g., <code>A←A+1</code>.
* Statements can be strung together on a line without a delimiter; e.g., <code>Note←APrintA</code>.
* An <code>If</code> statement can be used as a function, returning a value: <code>{{codett|2=cbmbas|Ver1←Ver1+IfVer1}}[[Modulo operation|Mod]]2{{codett|2=cbmbas|Then8}}{{codett|2=monkey|Else}}92</code>
* <code>If</code> statements can take an <code>Else</code> clause.

Special variable names:
* <code>Note</code> sounds a musical note, assigned numbers from 0 to 7
** Numbers assigned to <code>Note</code> are implicitly assigned modulus 8, thus 8 becomes 0, 9 becomes 1, etc.
* <code>Hor1</code>, <code>Hor2</code> - the horizontal coordinate of one of two squares
* <code>Ver1</code>, <code>Ver2</code> - the vertical coordinate of one of two squares

The language supports 26 unsigned integer variables A to Z. VCS BASIC supports integers from 0 to 99. Math operations wrap, so 99+1 becomes 0, 99+2 becomes 1, etc.

====Sample code====
The following example of a ''[[Pong]]'' game is provided.
{{pre|
1 Hor2←2+Key
2 {{codett|2=cbmbas|IfVer1>90ThenVer1←88}}
3 {{codett|2=cbmbas|IfHit}}{{codett|2=cbmbas|ThenVer1←9}}
4 {{codett|2=cbmbas|Ver1←Ver1+IfVer1}}[[Modulo operation|Mod]]2{{codett|2=cbmbas|Then8}}{{codett|2=monkey|Else}}92
5 Hor1←Hor1+7
6 {{codett|2=cbmbas|Goto1}}
}}