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162 lines
7.3 KiB
Plaintext
162 lines
7.3 KiB
Plaintext
Any [[Expression|expression]], including [[CONST|constants]] and [[Variable|variables]] all have an associated type to describe their value. QB64 has various built-in data types used to represent number and text values. [[#Numeric types|Numeric types]] represent number values, while [[#String types|string types]] represent text values.
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==Numeric types==
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QB64 supports several numeric types, capable of representing a wide range of numbers. There are two kinds of numeric data type: ''integer types'' and ''floating-point types''.
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===Integer types===
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Integer types represent integer (whole number) values, such as 1 and 100. They are divided into two flavors: ''signed'' and ''unsigned''.
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====Signed Integer types====
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Signed integers can represent positive and negative integer (whole number) values, such as 3, 10 and -16. These values are stored as a series of bits in [http://en.wikipedia.org/wiki/Two%27s_complement two's complement form], a common representation that makes them both straightforward and efficient to perform calculations with.
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Signed integers are typically used in simple mathematical equations.
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The range of values that these types can represent is based on their size, in bits; the greater number of bits, the larger positive and lesser negative value the types can represent.
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The signed integer types are: [[_BYTE]], [[INTEGER]], [[LONG]], [[_INTEGER64]] and [[_OFFSET]]
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{{CodeStart}}DIM n AS INTEGER
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n = -1
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PRINT n
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{{CodeEnd}}
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{{OutputStart}}-1
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{{OutputEnd}}
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====Unsigned Integer types====
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Unsigned integers can represent positive integer values only, such as 3, 10 and 16. These values are also stored as a series of bits, but unlike signed integers, all of the bits contribute to their value. Thus, these types can represent larger positive integer values than their signed counterparts.
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Unsigned integers are typically used to represent a simple quantity, like a ''count'' or a ''length''. They are also often used as ''bit masks'', where certain bits that make up the value represent separate information (such as the state of one or more ''flags'').
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Types: [[_UNSIGNED]] [[_BYTE]], [[_UNSIGNED]] [[INTEGER]], [[_UNSIGNED]] [[LONG]], [[_UNSIGNED]] [[_INTEGER64]], [[_UNSIGNED]] [[_OFFSET]]
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{{CodeStart}}' display the largest value representable by an _UNSIGNED INTEGER:
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DIM n AS _UNSIGNED INTEGER
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n = -1
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PRINT n
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{{CodeEnd}}
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{{OutputStart}}65535
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{{OutputEnd}}
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====_OFFSET Integer types====
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Offset Integer types can be any byte size integer value that can be used to designate pointer offset positions in memory. DO NOT TRANSFER offset values to other Integer types!
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===Floating-point types===
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Floating-point types can represent both positive and negative number values, as well as fractional number values, such as 1.2 and -34.56.
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Floating-point types are used in mathematical equations where fractional precision is important, such as trigonometry.
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The floating-point types are: [[SINGLE]], [[DOUBLE]] and [[_FLOAT]].
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{{CodeStart}}f! = 76.0
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c! = (5.0 / 9.0) * (f! - 32.0)
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PRINT f! ; "degrees Fahrenheit is" ; c! ; "degrees Celcius."
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{{CodeEnd}}
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{{OutputStart}} 76 degrees Fahrenheit is 24.44444 degrees Celcius.
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{{OutputEnd}}
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==String types==
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QB64 has built-in support for strings, which are contiguous sequences of characters represented as <tt>[[_UNSIGNED]] [[_BYTE]]</tt> values. Strings are usually used to store and manipulate text, but can also be used as a general storage area for arbitrary data (like a binary file).
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Strings have a property called ''length'', which is the number of characters currently stored in the string, and QB64 supports two kinds of string types based on this property: ''variable-length strings'' and ''fixed-length strings''.
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===Variable-length strings===
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Variable length strings are undefined length string variables. Fixed length strings MUST be defined in a program before they are used. Undefined strings can be up to 32767 characters in Qbasic.
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{{CodeStart}}
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message$ = "Hello"
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message$ = message$ + " world!" 'add to string variables using string concatenation only!
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PRINT message$
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{{CodeEnd}}
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{{OutputStart}}
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Hello world!
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{{OutputEnd}}
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===Fixed-length strings===
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Fixed length strings must be defined in a {{KW|DIM}} statement, {{KW|SUB}} or {{KW|FUNCTION}} parameter or {{KW|TYPE}} definition. The designated multiple is the maximum number of {{KW|STRING}} character bytes that the variable or {{KW|Arrays|array}} can hold. Excess bytes will not be included. No error is created.
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{{CodeStart}}
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DIM message AS STRING * 5
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message$ = "Hello"
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message$ = message$ + " world!"
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PRINT message$
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{{CodeEnd}}
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{{OutputStart}}
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Hello
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{{OutputEnd}}
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==Data type limits==
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The following table lists the numerical and string data types, their type suffix symbol, and the range of the values they can represent:
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'''Numerical types'''
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{| class="wikitable"
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! Type Name !! Type suffix symbol !! Minimum value !! Maximum value !! Size in Bytes
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|-
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| _BIT || ` || -1 || 0 || 1/8
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|-
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| _BIT * n || `n || -128 || 127 || n/8
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|-
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| _UNSIGNED _BIT || ~` || 0 || 1 || 1/8
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|-
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| _BYTE || %% || -128 || 127 || 1
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| _UNSIGNED _BYTE || ~%% || 0 || 255 || 1
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| INTEGER || % || -32,768 || 32,767 || 2
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| _UNSIGNED INTEGER || ~% || 0 || 65,535 || 2
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| LONG || & || -2,147,483,648 || 2,147,483,647 || 4
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| _UNSIGNED LONG || ~& || 0 || 4,294,967,295 || 4
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| _INTEGER64 || && || -9,223,372,036,854,775,808 || 9,223,372,036,854,775,807 || 8
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| _UNSIGNED _INTEGER64 || ~&& || 0 || 18,446,744,073,709,551,615 || 8
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| SINGLE || ! or none || -2.802597E-45 || +3.402823E+38 || 4
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|-
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| DOUBLE || # || -4.490656458412465E-324 || +1.797693134862310E+308 || 8
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| _FLOAT || ## || -1.18E-4932 || +1.18E+4932 || 32(10 used)
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|-
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| _OFFSET || %& || -9,223,372,036,854,775,808 || 9,223,372,036,854,775,807 || Use LEN
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|-
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| _UNSIGNED _OFFSET || ~%& || 0 || 18,446,744,073,709,551,615 || Use LEN
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| _MEM || none || combined memory variable type || N/A || Use LEN
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|}
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:''Note: For the floating-point numeric types [[SINGLE]] (default when not assigned), [[DOUBLE]] and [[_FLOAT]], the minimum values represent the smallest values closest to zero, while the maximum values represent the largest values closest to (+/-)infinity. OFFSET dot values are used as a part of the [[_MEM]] variable type in QB64 to return or set the position in memory.''
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'''String text type'''
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{| class="wikitable"
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! Type Name !! Type suffix symbol !! Minimum length !! Maximum length !! Size in Bytes
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| STRING || $ || 0 || 2,147,483,647 || Use LEN
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| STRING * n || $n || 1 || 2,147,483,647 || n
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|}
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''Note: For the fixed-length string type [[STRING|STRING * ''n'']], where ''n'' is an integer length value from 1 (one) to 2,147,483,647.
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==References==
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{{PageNavigation}}
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