C02/doc/c02vsC.txt

C02 for C programmers

TYPES

C02 only supports one data type: unsigned char.

POINTERS

C02 does not support pointer type variables or parameters. However, the
address-of operator may be used in function calls and the inline 
statement.

DIRECTIVES

C02 does not use a preprocessor. All directives are directly processed
by the compiler. C02 supports the directives #include and #pragma. The
directive #define is currently unimplemented and generates an error.
The #if, #else, and #endif directives are not recognized by C02.

CONSTANTS

The syntax of the const keyword in C02 differs from that use in standard C.
In C02, all constant names are prefixed with a # symbol.

ENUMERATION

The syntax of an enum statement in C02 is similar to standard C, except 
that no type name is specified and values may not be explicitly assigned
to the enumerated constants.

DECLARATIONS

Variable and function names may be no more than six characters in length. 
Multiple variable declarations separated by commas are allowed. 

A variable in a declaration may be initialized by following it with an
equal sign and a constant, however this declaration is done at compile
time, so no re-initialization will occur during code execution.

Array declarations using bracket syntax specify the upper bound, rather
than the array size. Therefore, the array will be allocated with one more
element than the specified number. 

Only one-dimensional arrays of type char are allowed and are limited to 
a total of 256 elements. Multi-dimensional arrays, arrays of arrays, and 
arrays of structs are not supported.

Struct definition and syntax is similar to standard C. When defining a 
struct, the char keyword is optional, since char the char type is implied.
Struct members may only be simple variables or arrays. The maximum total
size of a struct is 256 bytes. Initialization of members during declaration 
of a struct variable is not supported.  

REGISTERS

The 6502 registers may be explicitly referenced by name, i.e. A, X, and Y.
These may only be used in specific places due to the nature of the compiled
code a well as the limitations of the 6502 instruction set.

EXPRESSIONS

C02 supports the addition, subtraction, bitwise-and, bitwise-or, and 
exclusive-or operators. The multiplication, division, and binary shift
operators are not supported. These can be implemented through functions. 

Unary minus may only be used at the beginning of an expression, in which
case it is treated as a literal 0 and the subtraction operater, and the
term following the minus is used as the second term of the expression.

Functions calls may only be used in the first term of an expression.
However, the first argument of any function call may be any expression
(including one with a function call as the first term).

As in standard C, subscripted array elements may be used in any term of
an exptression  and the index may be any expression (including one with
a function call as the first term). 

The sizeof operator in C02 is the at sign @. It may only be used with
declared variables and struct members, not types.

CONDITIONALS

Conditional operations, including comparisons and logical operators,
may not be used within or in place of normal expressions, and are only
allowed in if, while, and for statements, as well as shortcut-ifs.

The comparison operators are ==, <, <=, >=, >, and <>. Unlike standard
C, the not-equals operator is <> instead of !=. In addition, = may be
substituted for ==. The logical not operator ! negates an entire 
comparison rather than an individual term within the comparison, thus 
the C02 code !b<x is equivalent to the C code !(b<x).

C02 uses the logical operators "and" and "or" instead of "&&" and "||",
and performs short-circuit evaluation of logical operators, making them
effectively right associative.  

FUNCTIONS

Parameter passing uses the 6502's A, Y, and X registers. This limits 
function calls to a maximum of three char variables or address reference
plus and optional char variable. However this also allows the return
of up to three char variables (see assignments below). However, the
non-standard push and pop statements allow explicit parameter passing
via the stack, and the inline keyword has been re-purposed to allow 
explicit passing of inline parameters. 

ASSIGNMENTS

Unlike standard C, struct contents may not be copied via simple assignment.
Struct variables may be copied byte by byte or using memory move functions.

Up to three comma-separated variables may be specified on the left side of
the = assignment operator. This is generally only useful when the expression
contains a function with multiple return values. 


STATEMENTS

Instead of the switch statement, C02 uses the select statement. The 
select statement works almost identically to the switch statement except
that case blocks do not fall through.