Differences from C

Syntax

Block comments /* */ are not supported, use line comments //.
You cannot put multiple statements on one line.
Semicolons are allowed at the end of the line, but no code can follow them.
There are no ++ or -- operators. Use += 1 and -= 1.
Pointer types are declared using the pointer. prefix, not * suffix. To dereference them, use p[0] instead of *p.
There is no unary & operator. Pointers to an object are acquired using the .pointer suffix. Raw addresses are acquired using the .addr suffix. The numeric values of the pointer and of the raw address may differ.
Operator precedence works differently. Bitwise and bit-shifting operators have the same precedence as arithmetic operators, and mixing different operators with the same precedence is usually forbidden. This prevents most ambiguities in bit-twiddling code, but requires care when porting code from or to C.
There is no ! operator. The negation is expressed as the not function.
The modulo operator is written %%. As with /, it's only defined for unsigned division.
The for loops are range-based. Arbitrary, C-like for loops are not supported.
Variable declaration and initialization have to be separate.
Integer literals starting with zero and containing just digits are decimal, not octal. For octal literals, use the 0o prefix.
String literals are not null-terminated by default. Use the z suffix for null-terminated strings.
Note: this is the opposite of what KickC does! Keep this in mind when migrating KickC code to Millfork or the other way around.
In if, do/while, while and for statements, parentheses are not required, but braces are. The else branch also requires braces, unless the only statement in the else block is an if statement.
There has to be a space between many operators and character literals, as the parser may treat the apostrophe as a part of the operator.

Preprocessor

The preprocessor cannot expand symbols to something more complex than an identifier or a literal.
The preprocessor cannot define symbols for use in other files.
The closest to C's #define is #use. Unlike #define, such definitions are not visible within the preprocessor.
Directives like #use and #pragma affect the entire file, not just the code after the directive.
The preprocessor cannot include files.

Semantics

There is no automatic integer promotion. An operation of two bytes will yield a byte. For example:
```
byte a
byte b
word w
w = a * b
```
may yield unexpected results. To prevent this, cast at least one argument:
```
w = word(a) * b
```
This issue applies mostly to the * and << operators.
There is no padding in structs, except before fields whose type is a struct or a union with a non-trivial alignment.