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| The different number types in Delphi |
| Delphi provides many different data types for storing numbers. Your choice depends on the data you want to handle. In general, smaller number capacities mean smaller variable sizes, and faster calculations. Ideally, you should use a type that comfortably copes with all possible values of the data it will store.
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| For example, a Byte type can comfortably hold the age of a person - no-one to date has lived as long as 255 years.
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| With decimal numbers, the smaller capacity types also have less precision. Less numbers of significant digits. Let us look at the different types:
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| Type Storage size Range
Byte 1 0 to 255
ShortInt 1 -127 to 127
Word 2 0 to 65,535
SmallInt 2 -32,768 to 32,767
LongWord 4 0 to 4,294,967,295
Cardinal 4* 0 to 4,294,967,295
LongInt 4 -2,147,483,648 to 2,147,483,647
Integer 4* -2,147,483,648 to 2,147,483,647
Int64 8 -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
Single 4 7 significant digits, exponent -38 to +38
Currency 8 50+ significant digits, fixed 4 decimal places
Double 8 15 significant digits, exponent -308 to +308
Extended 10 19 significant digits, exponent -4932 to +4932
* Note : the Integer and Cardinal types are both 4 bytes in size at present (Delphi release 7), but are not guaranteed to be this size in the future. All other type sizes are guaranteed.
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Assigning to and from number variables |
| Number variables can be assigned from constants, other numeric variables, and expressions:
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| const
YOUNG_AGE = 23; // Small integer constant
MANY = 300; // Bigger integer constant
RICH = 100000.00; // Decimal number : note no thousand commas
var
Age : Byte; // Smallest positive integer type
Books : SmallInt; // Bigger signed integer
Salary : Currency; // Decimal used to hold financial amounts
Expenses : Currency;
TakeHome : Currency;
begin
Age := YOUNG_AGE; // Assign from a predefined constant
Books := MANY + 45; // Assign from a mix of constants (expression)
Salary := RICH; // Assign from a predefined constant
Expenses := 12345.67; // Assign from a literal constant
TakeHome := Salary; // Assign from another variable
TakeHome := TakeHome - Expenses; // Assign from an expression
end;
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| Age is set to 23
Books is set to 345
Salary is set to 100000.00
Expenses is set to 12345.67
TakeHome is set to 87654.33
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Numerical operators |
| Number calculations, or expressions, have a number of primitive operators available:
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| + : Add one number to another
- : Subtract one number from another
* : Multiply two numbers
/ : Divide one decimal number by another
div : Divide one integer number by another
mod : Remainder from dividing one integer by another
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| When using these multiple operators in one expression, you should use round brackets to wrap around sub-expressions to ensure that the result is obtained. This is illustrated in the examples below:
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| var
myInt : Integer; // Define integer and decimal variables
myDec : Single;
begin
myInt := 20; // myInt is now 20
myInt := myInt + 10; // myInt is now 30
myInt := myInt - 5; // myInt is now 25
myInt := myInt * 4; // myInt is now 100
myInt := 14 div 3; // myInt is now 4 (14 / 3 = 4 remainder 2)
myInt := 14 mod 3; // myInt is now 2 (14 / 3 = 4 remainder 2)
myInt := 12 * 3 - 4; // myInt is now 32 (* comes before -)
myInt := 12 * (3 - 4); // myInt is now -12 (brackets come before *)
myDec := 2.222 / 2.0; // myDec is now 1.111
end;
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Numeric functions and procedures |
| Delphi provides many builtin functions and procedures that can perform numeric calculations. Some examples are given below - click on any to discover more. Note that these routines are stored in Units that are shipped with Delphi, and which form part of the standard delphi Run Time Library. You will need to include a reference to the Unit in order to use it (the code example provided with each gives the unit name and shows how to refer to it).
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| Abs Returns the absolute value of a signed number
Max Gives the maximum of two integer values
Min Gives the minimum of two integer values
Mean Gives the average of a set of numbers
Sqr Gives the square of a number
Sqrt Gives the square root of a number
Exp Gives the exponent of a number
Shl Shifts the bits in a number left
Shr Shifts the bits in a number right
Tan Gives the Tangent of a number
Cos Gives the Cosine of a number
Sin Gives the Sine of a number
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Converting from numbers to strings |
| Delphi also provides routines that convert numbers into strings. This is often useful for display purposes.
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| Str Converts a number to a string in a simple manner
CurrToStr Converts a Currency variable to a string
Format Number to string conversion with formatting
IntToStr Converts an integer to a string
IntToHex Converts a number into a hexadecimal string
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Converting from strings to numbers |
| Finally, Delphi provides string to number conversion utilities. Here are some examples:
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| StrToInt Converts an integer string into an integer
StrToIntDef Fault tolerant version of StrToInt
StrToFloat Converts a decimal string to a number
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