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Languages :: Pascal :: What's the difference?
By: barlow_g U.S.A.  Date: 19/04/2003 00:00:00  English  Points: 50 Status: Answered
Quality : Excellent
What's the difference between TYPE and VAR?
By: VGR Date: 19/04/2003 22:00:00 English  Type : Answer
Type defines a type, Var defines a variable :D

type == class
var == instance

Types : integer, record(struct), array, file of..., real(float),boolean...

var : a of type boolean, i of type integer, etc

thus :

type St4 = String[4];
Var ext_with_dot : St4;
Begin // program
ext_with_dot:='.TXT';
ext_with_dot:=3; // error because incompatible TYPES
End. // program
By: billious Date: 19/04/2003 22:14:00 English  Type : Assist
A TYPE is precisely what it says - a TYPE of variable. There are pre-defined TYPEs, such as byte, char and integer, and user-defined types where you build-your-own normally by combining pre-defined types into a RECORD.

A VAR is an instance of a type.

hence,

var
x : integer;
y : byte;
z : char;

establishes 3 different variables
x is an integer [value may be -(2**15) to ((2**15) - 1)]
y is a byte [value may be 0 to 255]
z is a char [single character]

To some extent, types may be compatible, so
x := y;
will always be ok since all possible values of y are within the range of possible values of x
but
y := x;
will not necessarily be ok beacuse some possible values of x are outside of the range of y.

y := z;
is nonsense because 'a' for instance (a character) is not representable as a number.

BUT
y := ord(z);
is fine because the ord function converts the single-character contained in z to the accepted numerical equivalent in the ASCII alphabet.

equally, z:=y; is nonsense, but z := asc(y); is fine. (asc is the reverse of the ord function)

HTH

...Bill
By: VGR Date: 19/04/2003 22:25:00 English  Type : Comment
let's call you verbi(lli)ous ;-)
By: billious Date: 19/04/2003 22:39:00 English  Type : Comment
VGR:
So I have a background in COBOL.

...Bill
By: VGR Date: 19/04/2003 23:15:00 English  Type : Comment
or FORTRAN, because of the (2**15) notation ;-)
By: Okey Date: 19/04/2003 23:52:00 English  Type : Comment
Type defines data structures for compiling!(not in exe)
Var uses existing or defined data struxctures,
which are created in exe!
By: VGR Date: 20/04/2003 00:01:00 English  Type : Comment
mouais 8-)

data structures are in the EXE (or COM ;-), at least by looking at the memory layout. You'll find the records' fields, the array elements, the strings and their length...

anyway, I don't want to polemicate
By: billious Date: 20/04/2003 00:31:00 English  Type : Comment
VGR:

Yeah, FORTRAN too Second language I learnt, after Assembler. Not used it commercially for nearly 20 years. Interesting how notation conventions are observed across languages.

...Bill
By: OpConsole Date: 08/09/2003 13:03:00 English  Type : Comment
barlow_g:
This old question needs to be finalized -- accept an answer, split points, or get a refund.
By: VGR Date: 09/09/2003 06:42:00 English  Type : Comment
given the proximity in time, I suggest a fair split

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