Editing BASIC (section)

=== Examples ===
[[File:ARROW (Listing) (3300726999).png|thumb|A simple game implemented in BASIC]]

==== Unstructured BASIC ====
New BASIC programmers on a home computer might start with a simple program, perhaps using the language's PRINT statement to display a message on the screen; a well-known and often-replicated example is [[The C Programming Language|Kernighan and Ritchie]]'s [["Hello, World!" program]]:

<syntaxhighlight lang="basic">
10 PRINT "Hello, World!"
20 END
</syntaxhighlight>

An [[infinite loop]] could be used to fill the display with the message:

<syntaxhighlight lang="basic">
10 PRINT "Hello, World!"
20 GOTO 10
</syntaxhighlight>

Note that the <code>END</code> statement is optional and has no action in most dialects of BASIC. It was not always included, as is the case in this example. This same program can be modified to print a fixed number of messages using the common <code>FOR...NEXT</code> statement:

<syntaxhighlight lang="basic">
10 LET N=10
20 FOR I=1 TO N
30 PRINT "Hello, World!"
40 NEXT I
</syntaxhighlight>

Most home computers BASIC versions, such as [[MSX BASIC]] and [[GW-BASIC]], supported simple data types, loop cycles, and arrays. The following example is written for GW-BASIC, but will work in most versions of BASIC with minimal changes:

<syntaxhighlight lang="basic">
10 INPUT "What is your name: "; U$
20 PRINT "Hello "; U$
30 INPUT "How many stars do you want: "; N
40 S$ = ""
50 FOR I = 1 TO N
60 S$ = S$ + "*"
70 NEXT I
80 PRINT S$
90 INPUT "Do you want more stars? "; A$
100 IF LEN(A$) = 0 THEN GOTO 90
110 A$ = LEFT$(A$, 1)
120 IF A$ = "Y" OR A$ = "y" THEN GOTO 30
130 PRINT "Goodbye "; U$
140 END
</syntaxhighlight>
The resulting dialog might resemble:

 What is your name: Mike
 Hello Mike
 How many stars do you want: 7
 *******
 Do you want more stars? yes
 How many stars do you want: 3
 ***
 Do you want more stars? no
 Goodbye Mike

The original Dartmouth Basic was unusual in having a matrix keyword, MAT.{{efn|From version 3 onwards.}} Although not implemented by most later microprocessor derivatives, it is used in this example from the 1968 manual<ref>{{Cite book|url=http://bitsavers.trailing-edge.com/pdf/dartmouth/BASIC_4th_Edition_Jan68.pdf |archive-url=https://web.archive.org/web/20140103140704/http://bitsavers.trailing-edge.com/pdf/dartmouth/BASIC_4th_Edition_Jan68.pdf |archive-date=2014-01-03 |url-status=live|title=Basic: a manual for BASIC, the elementary algebraic language designed for use with the Dartmouth Time Sharing System|last1=Kemeny|first1=John G.|last2=Kurtz|first2=Thomas E.|date=January 1968|publisher=Dartmouth College Computation Center|location=Hanover, N.H.|language=en|edition=4th|page=53}}</ref> which averages the numbers that are input:

<syntaxhighlight lang="basic">
5 LET S = 0
10 MAT INPUT V 
20 LET N = NUM 
30 IF N = 0 THEN 99 
40 FOR I = 1 TO N 
45 LET S = S + V(I) 
50 NEXT I 
60 PRINT S/N 
70 GO TO 5 
99 END
</syntaxhighlight>

==== Structured BASIC ====
Second-generation BASICs (for example, [[VSI BASIC for OpenVMS|VAX Basic]], [[SuperBASIC]], [[True BASIC]], [[QuickBASIC]], [[BBC BASIC]], [[Pick operating system|Pick BASIC]], [[PowerBASIC]], [[Liberty BASIC]], [[QB64]] and (arguably) [[COMAL]]) introduced a number of features into the language, primarily related to structured and procedure-oriented programming. Usually, [[line number]]ing is omitted from the language and replaced with [[label (computer science)|labels]] (for [[GOTO]]) and [[subroutine|procedures]] to encourage easier and more flexible design.<ref name="GBvsQB">{{cite web|url=http://support.microsoft.com/kb/73084|title=Differences Between GW-BASIC and QBasic|date=2003-05-12|access-date=2008-06-28|archive-url=https://web.archive.org/web/20131019181140/http://support.microsoft.com/kb/73084|archive-date=2013-10-19}}</ref> In addition keywords and structures to support repetition, selection and procedures with local variables were introduced.

The following example is in Microsoft QuickBASIC:

<syntaxhighlight lang="QBasic">
REM QuickBASIC example

REM Forward declaration - allows the main code to call a
REM    subroutine that is defined later in the source code
DECLARE SUB PrintSomeStars (StarCount!)

REM Main program follows
INPUT "What is your name: ", UserName$
PRINT "Hello "; UserName$
DO
   INPUT "How many stars do you want: ", NumStars
   CALL PrintSomeStars(NumStars)
   DO
      INPUT "Do you want more stars? ", Answer$
   LOOP UNTIL Answer$ <> ""
   Answer$ = LEFT$(Answer$, 1)
LOOP WHILE UCASE$(Answer$) = "Y"
PRINT "Goodbye "; UserName$
END

REM subroutine definition
SUB PrintSomeStars (StarCount)
   REM This procedure uses a local variable called Stars$
   Stars$ = STRING$(StarCount, "*")
   PRINT Stars$
END SUB
</syntaxhighlight>

==== Object-oriented BASIC ====
Third-generation BASIC dialects such as [[Visual Basic (classic)|Visual Basic]], [[Xojo]], [[Gambas]], [[StarOffice Basic]], [[BlitzMax]] and [[PureBasic]] introduced features to support object-oriented and [[event-driven programming]] paradigm. Most built-in procedures and functions are now represented as ''methods'' of standard objects rather than ''operators''. Also, the [[operating system]] became increasingly accessible to the BASIC language.

The following example is in [[Visual Basic .NET]]:

<!-- needs a better (event-driven?) example -->
<syntaxhighlight lang="vbnet">
Public Module StarsProgram
   Private Function Ask(prompt As String) As String
      Console.Write(prompt)
      Return Console.ReadLine()
   End Function

   Public Sub Main()
      Dim userName = Ask("What is your name: ")
      Console.WriteLine("Hello {0}", userName)

      Dim answer As String

      Do
         Dim numStars = CInt(Ask("How many stars do you want: "))
         Dim stars As New String("*"c, numStars)
         Console.WriteLine(stars)

         Do
            answer = Ask("Do you want more stars? ")
         Loop Until answer <> ""
      Loop While answer.StartsWith("Y", StringComparison.OrdinalIgnoreCase)

      Console.WriteLine("Goodbye {0}", userName)
   End Sub
End Module
</syntaxhighlight>