Chapter 5: Basic Values & Data

Level 1 — Acquaintance

The foundation of all computation: types, values, and how C and Auto represent data.

This is the most important chapter in Level 1. Everything you build in C or Auto rests on understanding how the language represents values in memory. We cover the abstract machine model, basic types, conversions, initializers, named constants, and binary representations.

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5.1 The Abstract State Machine

C Deep Dive: The C standard does not describe a physical computer. Instead it defines an abstract state machine that specifies what a conforming program must do. A real compiler's job is to produce code that behaves as if the abstract machine executed the program.

The abstract machine has:

• Objects — regions of storage that hold values (variables, allocated memory).
• Values — the bit patterns stored in objects, interpreted according to their type.
• Side effects — changes to the state of the machine (writing to a variable, calling an I/O function).
• Sequence points — moments when all preceding side effects are guaranteed complete.

When you write int x = 42;, the abstract machine:

1. Allocates storage for an object named x.
2. Determines that its type is int.
3. Stores the value 42 in that object.

Auto simplifies this model by removing undefined behavior. If an Auto program compiles, it has well-defined semantics. The trade-off is that Auto hides certain machine-level details that C exposes (such as raw pointer arithmetic and exact object layout).

Takeaway: C's abstract machine is a contract between you and the compiler. Stay within the contract and your code is portable and predictable. Violate it (e.g., via undefined behavior) and the compiler is free to do anything.

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5.2 Basic Types

C has a small but nuanced set of fundamental types. Auto maps them to a cleaner subset:

C type	Auto type	Size (typical)	Notes
char	char	1 byte	Character or small integer
signed char	i8	1 byte	Explicitly signed 8-bit
unsigned char	u8	1 byte	Unsigned 8-bit
short	i16	2 bytes	Short integer
int	int	4 bytes	Default integer
long	i64	4 or 8 bytes	Platform-dependent
long long	i64	8 bytes	At least 64-bit
float	float	4 bytes	Single-precision IEEE 754
double	float	8 bytes	Double-precision; Auto uses float for both
_Bool	bool	1 byte	C99 boolean; Auto has bool
size_t	usize	4 or 8 bytes	Unsigned, sizeof result

Key differences:

• C's double is distinct from float. Auto unifies them as float and lets the compiler choose the precision.
• C has signed/unsigned variants for every integer type. Auto defaults to signed and provides explicit u8, u16, u32, u64 for unsigned needs.
• C's char may be signed or unsigned depending on the platform. Auto treats char as a distinct type for character data only.