Basic

Appeared in:
1964
Influenced:
Paradigm:
Typing discipline:
File extensions:
.bas
Versions and implementations (Collapse all | Expand all):
Programming language

BASIC (“Beginner’s All-purpose Symbolic Instruction Code”) is a family of high-level programming languages.

The first language of the family, Dartmouth Basic was created in 1964. Its purpose was to facilitate teaching computer science and using computers for research purposes for people without special background. Its main design principle was to be simple enough for beginners (in particular, to require no hardware or operating system understanding) and advanced enough for professionals (in particular, to be general-purpose). Its authors put a lot of effort in its promotion, so it became rather widespread and spawned a lot of implementations.

Since Basic is not a single language but a family of languages which vary a lot, the paradigms supported by the languages of the family vary just as much. Thus, early Basic implementations (the original Dartmouth Basic and its contemporaries) allowed only non-structured programming. Years later new dialects introduced means for structured and procedural programming, which were quickly becoming generally adopted paradigms. Finally, Microsoft Visual Basic along with its successor Microsoft Visual Basic .NET and scripting language VBA support object-oriented and event-driven programming and bear little resemblance to their ancestor. The only thing which unites all Basic dialects is their syntax, though even it has changed quite a lot since first implementation.

Basic has two major official standards — “Minimal Basic” (ANSI X3.60-1978 and ISO/IEC 6373:1984) and “Full Basic” (ANSI X3.113-1987 and INCITS/ISO/IEC 10279-1991 (R2005)).

Early Basic dialects have died out long ago, but modern dialects of the family (mainly Visual Basic and VB.NET) retain traditional popularity of the language.

Elements of syntax:

Inline comments REM (original Basic), ' (Visual Basic)
Case-sensitivity no
Variable assignment varname = value
Variable declaration Dim varname As type
Variable declaration with assignment Dim varname As type = value
Deep equality a = b
Deep inequality a <> b
Comparison < > <= >=
Function definition Sub functionName (argname1 As argtype1, ..., argnameN As argtypeN) ... End Sub
Function call functionName(arg1, ..., argN)
Function call with no parameters functionName()
If - then If condition Then trueBlock End If
If - then - else If condition Then trueBlock Else falseBlock End If
Loop forever Do While true loopBody Loop
While condition do Do While condition loopBody Loop
Do until condition Do loopBody Loop Until condition
For each value in a numeric range, 1 increment For i = first To last Step 1 loopBody Next i

Examples:

Hello, World!:

Example for versions Microsoft Visual Basic 6

The intended use of Visual Basic is GUI applications development, so creating a simple console application is a non-trivial task itself. This example features:

  • importing required functions from standard library;
  • console creation;
  • getting the handle of console output stream;
  • writing the message to this stream and
  • deallocation of used objects. 
Option Explicit

    Declare Function AllocConsole Lib "kernel32" () As Long
    Declare Function FreeConsole Lib "kernel32" () As Long
    Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
    Declare Function GetStdHandle Lib "kernel32" (ByVal nStdHandle As Long) As Long
    Declare Function WriteConsole Lib "kernel32" Alias "WriteConsoleA" _
           (ByVal hConsoleOutput As Long, lpBuffer As Any, ByVal _
           nNumberOfCharsToWrite As Long, lpNumberOfCharsWritten As Long, _
           lpReserved As Any) As Long
    Declare Function Sleep Lib "kernel32" (ByVal dwMilliseconds As Long) As Long

Private Sub Main()
    'create a console instance
    AllocConsole
    'get handle of console output
    Dim hOut As Long
    hOut = GetStdHandle(-11&)
    'output string to console output
    Dim s As String
    s = "Hello, World!" & vbCrLf
    WriteConsole hOut, ByVal s, Len(s), vbNull, vbNull
    'make a pause to look at the output
    Sleep 2000
    'close the handle and destroy the console
    CloseHandle hOut
    FreeConsole
End Sub

Factorial:

Example for versions Microsoft Visual Basic 6

This example uses iterative factorial definition. Trying to calculate 13! produces an arithmetic overflow error, so program output ends with line “12! = 479001600”. After this a message “Run-time error ‘6’: Overflow” pops up. 

Option Explicit

    Declare Function AllocConsole Lib "kernel32" () As Long
    Declare Function FreeConsole Lib "kernel32" () As Long
    Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
    Declare Function GetStdHandle Lib "kernel32" (ByVal nStdHandle As Long) As Long
    Declare Function WriteConsole Lib "kernel32" Alias "WriteConsoleA" _
           (ByVal hConsoleOutput As Long, lpBuffer As Any, ByVal _
           nNumberOfCharsToWrite As Long, lpNumberOfCharsWritten As Long, _
           lpReserved As Any) As Long
    Declare Function Sleep Lib "kernel32" (ByVal dwMilliseconds As Long) As Long

Private Sub Main()
    'create a console instance
    AllocConsole
    'get handle of console output
    Dim hOut As Long
    hOut = GetStdHandle(-11&)
    'output string to console output
    Dim s As String
    Dim i As Integer
    Dim f As Long
    f = 1
    s = "0! = 1" & vbCrLf
    WriteConsole hOut, ByVal s, Len(s), vbNull, vbNull
    For i = 1 To 16 Step 1
        f = f * i
        s = i & "! = " & f & vbCrLf
        WriteConsole hOut, ByVal s, Len(s), vbNull, vbNull
    Next i
    'make a pause to look at the output
    Sleep 2000
    'close the handle and destroy the console
    CloseHandle hOut
    FreeConsole
End Sub

Fibonacci numbers:

Example for versions Microsoft Visual Basic 6

This example uses recursive definition of Fibonacci numbers. 

Option Explicit

    Declare Function AllocConsole Lib "kernel32" () As Long
    Declare Function FreeConsole Lib "kernel32" () As Long
    Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
    Declare Function GetStdHandle Lib "kernel32" (ByVal nStdHandle As Long) As Long
    Declare Function WriteConsole Lib "kernel32" Alias "WriteConsoleA" _
           (ByVal hConsoleOutput As Long, lpBuffer As Any, ByVal _
           nNumberOfCharsToWrite As Long, lpNumberOfCharsWritten As Long, _
           lpReserved As Any) As Long
    Declare Function Sleep Lib "kernel32" (ByVal dwMilliseconds As Long) As Long

Public Function Fibonacci(ByVal n As Integer) As Integer
    If (n <= 2) Then
        Fibonacci = 1
    Else
        Fibonacci = Fibonacci(n - 1) + Fibonacci(n - 2)
    End If
End Function

Private Sub Main()
    'create a console instance
    AllocConsole
    'get handle of console output
    Dim hOut As Long
    hOut = GetStdHandle(-11&)
    'output string to console output
    Dim s As String
    Dim i As Integer
    For i = 1 To 16 Step 1
        s = Fibonacci(i) & ", "
        WriteConsole hOut, ByVal s, Len(s), vbNull, vbNull
    Next i
    s = "..." & vbCrLf
    WriteConsole hOut, ByVal s, Len(s), vbNull, vbNull
    'make a pause to look at the output
    Sleep 2000
    'close the handle and destroy the console
    CloseHandle hOut
    FreeConsole
End Sub

Hello, World!:

Example for versions QBasic 1.1, QuickBASIC 4.5 
PRINT "Hello, World!"

Factorial:

Example for versions QBasic 1.1, QuickBASIC 4.5

This example uses recursive factorial definition.

The default data type for calculations is floating point, so program output looks like this:
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
10! = 3628800
11! = 3.99168Е+07
12! = 4.790016Е+08
13! = 6.227021Е+09
14! = 8.717829Е+10
15! = 1.307674Е+12
16! = 2.092279Е+13 

DECLARE FUNCTION factorial (n)

FOR i = 0 TO 16:
    PRINT STR$(i) + "! =" + STR$(factorial(i))
NEXT i
END

FUNCTION factorial (n)
    IF n = 0 THEN
        factorial = 1
    ELSE
        factorial = n * factorial(n - 1)
    END IF
END FUNCTION

Fibonacci numbers:

Example for versions QBasic 1.1, QuickBASIC 4.5

Numbers which have already been calculated are stored in array F and are retrieved from it to calculate the next ones. To get program output in required format, the numbers in the array are concatenated to form one string with required delimiters. STR$ function converts a number to a string. 

DIM F(16)
F(1) = 1
F(2) = 1
FOR i = 3 TO 16:
    F(i) = F(i - 1) + F(i - 2)
NEXT i
DIM S AS STRING
S = ""
FOR i = 1 TO 16:
    S = S + STR$(F(i)) + ", "
NEXT i
S = S + "..."
PRINT S

Fibonacci numbers:

Example for versions QBasic 1.1, QuickBASIC 4.5

This example uses recursive definition of Fibonacci numbers. Each call of PRINT function prints the arguments to a separate line and adds a space before and after printed number, so program output looks like this:
1 ,
1 ,
2 ,
3 ,
5 ,
8 ,
13 ,
21 ,
34 ,
55 ,
89 ,
144 ,
233 ,
377 ,
610 ,
987 ,
… 

DECLARE FUNCTION fibonacci (n)

FOR i = 1 TO 16:
    PRINT fibonacci(i); ", "
NEXT i
PRINT "..."

FUNCTION fibonacci (n)
    IF (n <= 2) THEN
        fibonacci = 1
    ELSE
        fibonacci = fibonacci(n - 1) + fibonacci(n - 2)
    END IF
END FUNCTION

Fibonacci numbers:

Example for versions QBasic 1.1, QuickBASIC 4.5

Fibonacci numbers are calculated using Binet’s formula. The resulting numbers can differ from actual ones slightly due to calculation imprecision; to remove this effect, we use function INT which truncates fractional part of the number. 

DECLARE FUNCTION FIBONACCI (n)

DIM S AS STRING
S = ""
FOR i = 1 TO 16:
    S = S + STR$(INT(FIBONACCI(i) + .1)) + ","
NEXT i
S = S + "..."
PRINT S

FUNCTION FIBONACCI (n)
    p1 = ((1 + SQR(5)) * .5) ^ n
    p2 = ((1 - SQR(5)) * .5) ^ n
    FIBONACCI = (p1 - p2) / SQR(5)
END FUNCTION

Hello, World!:

Example for versions Microsoft Visual Basic .NET 9 (2008) 
Module Module1
    Sub Main()
        Console.WriteLine("Hello, World!")
    End Sub
End Module

Factorial:

Example for versions Microsoft Visual Basic .NET 9 (2008)

This example uses recursive factorial definition. 

Module Module1
    Function Factorial(ByVal n As Integer) As Long
        If n = 0 Then
            Return 1
        Else
            Return n * Factorial(n - 1)
        End If
    End Function

    Sub Main()
        For i As Integer = 0 To 16
            Console.WriteLine(i & "! = " & Factorial(i))
        Next
    End Sub
End Module

Fibonacci numbers:

Example for versions Microsoft Visual Basic .NET 9 (2008)

This example uses recursive definition of Fibonacci numbers. 

Module Module1
    Function Fibonacci(ByVal n As Integer) As Long
        If n < 3 Then
            Return 1
        Else
            Return Fibonacci(n - 1) + Fibonacci(n - 2)
        End If
    End Function

    Sub Main()
        For i As Integer = 1 To 16
            Console.Write(Fibonacci(i) & ", ")
        Next
        Console.WriteLine("...")
    End Sub
End Module

Quadratic equation:

Example for versions Microsoft Visual Basic .NET 9 (2008) 
Module Module1
    Sub Main()
        Dim A, B, C, D As Integer
        Dim p1, p2 As Double
        Try
            Console.Write("A = ")
            A = Val(Console.ReadLine())
            Console.Write("B = ")
            B = Val(Console.ReadLine())
            Console.Write("C = ")
            C = Val(Console.ReadLine())
        Catch ex As Exception
            Console.WriteLine("Invalid input.")
            Return
        End Try
        If A = 0 Then
            Console.WriteLine("Not a quadratic equation.")
            Return
        End If
        D = B * B - 4 * A * C
        p1 = -B / 2.0 / A
        p2 = Math.Sqrt(Math.Abs(D)) / 2.0 / A
        If D = 0 Then
            Console.Write("x = " & p1.ToString())
        ElseIf D > 0 Then
            Console.WriteLine("x1 = " & (p1 + p2).ToString())
            Console.WriteLine("x2 = " & (p1 - p2).ToString())
        Else
            Console.WriteLine("x1 = (" & p1.ToString() & "," & p2.ToString() & ")")
            Console.WriteLine("x2 = (" & p1.ToString() & ",-" & p2.ToString() & ")")
        End If
    End Sub
End Module

Quadratic equation:

Example for versions QuickBASIC 4.5 
PRINT "A = "
INPUT A
IF (A = 0) THEN
    PRINT "Not a quadratic equation."
ELSE
    PRINT "B = "
    INPUT B
    PRINT "C = "
    INPUT C
    D = B * B - 4 * A * C
    IF (D = 0) THEN
        PRINT "x = " + STR$(-B / 2! / A)
    ELSE
        IF (D > 0) THEN
            PRINT "x1 = " + STR$((-B + SQR(D)) / 2! / A)
            PRINT "x2 = " + STR$((-B - SQR(D)) / 2! / A)
        ELSE
            PRINT "x1 = (" + STR$(-B / 2! / A) + "," + STR$(SQR(-D) / 2! / A) + ")"
            PRINT "x2 = (" + STR$(-B / 2! / A) + "," + STR$(-SQR(-D) / 2! / A) + ")"
        END IF
    END IF
END IF