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Notes on C's abstract state machine and basic types.

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Joshua Potter 2024-08-16 19:46:05 -06:00
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@ -8,4 +8,5 @@ title: "2024-08-16"
- [ ] Sheet Music (10 min.)
- [ ] Korean (Read 1 Story)
* Notes on [[relations#Preorders|preorders]] and [[relations#Partial Orders|partial orders]].
* Notes on [[relations#Preorders|preorders]] and [[relations#Partial Orders|partial orders]].
* Details on C's [[c17/index|abstract state machine]] and [[types|integer types]].

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@ -498,14 +498,6 @@ Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Program
<!--ID: 1707493017237-->
END%%
%%ANKI
Basic
Is declaration `char` signed or unsigned?
Back: This is implementation-dependent.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1707493017239-->
END%%
%%ANKI
Cloze
{1:`float`} has {2:4} byte precision whereas {2:`double`} has {1:8} byte precision.
@ -703,211 +695,6 @@ Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Progra
<!--ID: 1722786892138-->
END%%
## Integer Literals
Negative integer literals are typed in a counterintuitive way. When the compiler sees a number of form `-X`, the type of `X` is determined *before* being negated. Promotion rules are as follows:
Decimal | Other Bases
----------- | --------------------
`int` | `int`
`long` | `unsigned`
`long long` | `long`
`-` | `unsigned long`
`-` | `long long`
`-` | `unsigned long long`
%%ANKI
Basic
How does the compiler process integer literal `-X`?
Back: By first determining the type of `X` and then negating the value.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820805-->
END%%
%%ANKI
Basic
What integer literals are guaranteed `signed`?
Back: Decimal integer constants.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820826-->
END%%
%%ANKI
Basic
How do we specify an octal integer literal?
Back: Prepend the literal with a `0`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1710673807992-->
END%%
%%ANKI
Basic
Why avoid negative octal integer literals?
Back: Depending on value, the resulting type may be `unsigned`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820829-->
END%%
%%ANKI
Basic
How do we specify a hexadecimal integer literal?
Back: Prepend the literal with a `0x` or `0X`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1710673807995-->
END%%
%%ANKI
Cloze
Octal literals are to {`0`} whereas hexadecimal literals are to {`0x`/`0X`}.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1710673807997-->
END%%
%%ANKI
Basic
How might C dangerously interpret a negative hexadecimal integer literal?
Back: Depending on the value, the resulting type may be `unsigned`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820833-->
END%%
%%ANKI
Basic
Which header file contains `INT_MAX`?
Back: `<limits.h>`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708615249864-->
END%%
%%ANKI
Cloze
{`INT_MAX`} is to `signed` whereas {`UINT_MAX`} is to `unsigned`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820837-->
END%%
%%ANKI
Basic
How does `<limits.h>` define `INT_MIN`?
Back: As `(-INT_MAX - 1)`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820840-->
END%%
%%ANKI
Basic
*Why* is `INT_MIN` defined as `(-INT_MAX - 1)` instead of directly as e.g. `-2147483648`?
Back: Because `2147483648` (without `-`) would be sized as a non-`int` before being negated.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820843-->
END%%
%%ANKI
Cloze
`INT_MAX` is to {`<limits.h>`} whereas `INT32_MAX` is to {`<stdint.h>`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708615249873-->
END%%
%%ANKI
Basic
What suffix can be used to denote an `unsigned` integer literal?
Back: Case-insensitive `U`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708615249876-->
END%%
%%ANKI
Basic
What suffix can be used to denote a `long` integer literal?
Back: Case-insensitive `L`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820847-->
END%%
%%ANKI
Basic
What suffix can be used to denote a `long long` integer literal?
Back: Case-insensitive `LL`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820850-->
END%%
%%ANKI
Basic
What suffix can be used to denote an `unsigned long long` integer literal?
Back: Case-insensitive `ULL`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820856-->
END%%
%%ANKI
Basic
In what order does C cast size and "signedness"?
Back: C casts size then signedness.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608760-->
END%%
%%ANKI
Basic
In what order does C cast "signedness" and size?
Back: C casts size then signedness.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677626482-->
END%%
%%ANKI
Basic
Given `short sx`, cast `(unsigned) sx` is more explicitly written as what other sequence of casts?
Back: `(unsigned) (int) sx`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608762-->
END%%
%%ANKI
Basic
Given `short sx`, are the following two lines equivalent?
```c
(unsigned) sx
(unsigned) (int) sx
```
Back: Yes.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608764-->
END%%
%%ANKI
Basic
Given `short sx`, are the following two lines equivalent?
```c
(unsigned) sx
(unsigned) (unsigned short) sx
```
Back: No.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608766-->
END%%
%%ANKI
Basic
Given `short sx`, why is the following not an identity?
```c
(unsigned) sx = (unsigned) (unsigned short) sx
```
Back: `(unsigned) sx` casts size before "signedness".
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608767-->
END%%
%%ANKI
Basic
What does "signedness" of a variable refer to?
Back: Whether the variable was declared `signed` or `unsigned`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608769-->
END%%
## Bibliography
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.

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@ -8,14 +8,59 @@ tags:
## Overview
An **object** is a region of data storage in the execution environment, the contents of which can represent **values**. We say an object type is **complete** if there is sufficient information to determine the size of objects of that type. Otherwise we say it is **incomplete**.
> A C program can be seen as a sort of machine that manipulates values: the particular values that variables of the program have at a given time, and also intermediate values that are the result of computed expressions.
An **lvalue** is an expression (with non-`void` object type) that potentially designates an object. An **rvalue** is the "value of the expression."
This quote describes C's **abstract state machine**. Whatever instructions a C program compiles down to is "unimportant" provided that all **observable states** are correctly reproduced. This is the essence of optimization.
%%ANKI
Basic
What feature of C's abstract state machine makes C performant?
Back: It enables optimization.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661330-->
END%%
%%ANKI
Basic
C can compile into any sequence of instructions provided what holds?
Back: All observable states are correctly reproduced.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661337-->
END%%
%%ANKI
Basic
Why is C's abstract state machine called the way it is?
Back: Compilers are free to realize the state machine however they see fit.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661340-->
END%%
%%ANKI
Basic
What three components make up C's abstract state machine?
Back: Values, types, and binary representations.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661343-->
END%%
%%ANKI
Cloze
In C's abstract state machine, {binary representations} describe {types} which describe {values}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856668033-->
END%%
## Values
An **object** is a region of data storage in the execution environment, the contents of which can represent **values**. An **lvalue** is an expression (with non-`void` object type) that potentially designates an object. An **rvalue** is the "value of the expression."
The notion of a value in C is an abstract entity. It exists beyond the program or the representation of the value in the program. For example, the value `0` (no matter how its represented) added to variable `x` should always yield result `x` regardless of platform.
%%ANKI
Basic
What does an object refer to?
Back: A region of data storage in the execution environment, the contents of which can represent values.
Back: A region of data storage in the execution environment.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994830-->
END%%
@ -28,6 +73,22 @@ Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70
<!--ID: 1723510994835-->
END%%
%%ANKI
Basic
Why does Gustedt refer to values as abstract entities?
Back: A value exists beyond a program or any particular representation.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661349-->
END%%
%%ANKI
Basic
How does Gustedt distinguish the data of a program execution from values?
Back: The data is the set of values of all objects at a given moment.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661358-->
END%%
%%ANKI
Cloze
A {value} refers to the contents of an {object} when interpreted as having a specific type.
@ -35,54 +96,6 @@ Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70
<!--ID: 1723510994839-->
END%%
%%ANKI
Basic
Types are partitioned into what two categories?
Back: Object types and function types.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994842-->
END%%
%%ANKI
Basic
What is an object type?
Back: A type that describes objects.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994846-->
END%%
%%ANKI
Basic
What is a function type?
Back: A type that describes functions.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994851-->
END%%
%%ANKI
Basic
What two parts characterize a function type?
Back: The return type and the number/types of its parameters.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994856-->
END%%
%%ANKI
Basic
What does it mean for an object type to be complete?
Back: There is sufficient information to determine the size of objects of that type.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994866-->
END%%
%%ANKI
Basic
What does it mean for an object type to be incomplete?
Back: There is insufficient information to determine the size of objects of that type.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994870-->
END%%
%%ANKI
Basic
What is an lvalue?
@ -115,22 +128,6 @@ Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70
<!--ID: 1723510994886-->
END%%
%%ANKI
Basic
What object type can an lvalue *not* have?
Back: `void`
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994890-->
END%%
%%ANKI
Basic
What object type can an lvalue have?
Back: Any object type other than `void`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994895-->
END%%
%%ANKI
Basic
Can an lvalue designate an object?
@ -336,6 +333,67 @@ Reference: ISO: Programming Languages - C,” April 12, 2011, [https://port70.ne
<!--ID: 1723510995006-->
END%%
## Types
Types are additional properties that C associates with values. All values have a type that is statically determined and all possible operations on a value are determined by its type.
Types are categorized as function types and object types. An object type is **complete** if there is sufficient information to determine the size of objects of that type. Otherwise we say it is **incomplete**.
%%ANKI
Cloze
Possible operations on a {value} are determined by its {type}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661364-->
END%%
%%ANKI
Basic
Types are partitioned into what two categories?
Back: Object types and function types.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994842-->
END%%
%%ANKI
Basic
What is an object type?
Back: A type that describes objects.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994846-->
END%%
%%ANKI
Basic
What is a function type?
Back: A type that describes functions.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994851-->
END%%
%%ANKI
Basic
What two parts characterize a function type?
Back: The return type and the number/types of its parameters.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994856-->
END%%
%%ANKI
Basic
What does it mean for an object type to be complete?
Back: There is sufficient information to determine the size of objects of that type.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994866-->
END%%
%%ANKI
Basic
What does it mean for an object type to be incomplete?
Back: There is insufficient information to determine the size of objects of that type.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994870-->
END%%
%%ANKI
Basic
Does `x` have complete or incomplete object type in the following?
@ -369,6 +427,72 @@ Reference: ISO: Programming Languages - C,” April 12, 2011, [https://port70.ne
<!--ID: 1723510995023-->
END%%
%%ANKI
Basic
What object type can an lvalue *not* have?
Back: `void`
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994890-->
END%%
%%ANKI
Basic
What object type can an lvalue have?
Back: Any object type other than `void`.
Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
<!--ID: 1723510994895-->
END%%
## Representation
The **binary representation** of a type is the model used to represent values of said type on a given platform. The **object representation** of a type determines how values are stored in memory, disk, etc.
%%ANKI
Basic
What is the binary representation of a type?
Back: The model used to represent values of the type on a given platform.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661371-->
END%%
%%ANKI
Basic
What is the binary representation of a value?
Back: N/A. Binary representations describe types not values.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661379-->
END%%
%%ANKI
Basic
What is the object representation of a type?
Back: How a value of a given type is actually stored in memory, disk, etc.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661386-->
END%%
%%ANKI
Cloze
A {type}'s {binary representation} determines the results of all operations.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661393-->
END%%
%%ANKI
Basic
Why does Gustedt refer to binary representations as abstract entities?
Back: Binary representations don't completely determine how values are stored in memory.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661399-->
END%%
%%ANKI
Cloze
A {binary} representation is abstract whereas an {object} representation is concrete.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723856661405-->
END%%
## Bibliography
* “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).

418
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@ -6,4 +6,420 @@ tags:
- c17
---
## Overview
## Overview
C has a series of basic types and means of constructing derived types from them.
## Integers
Type `char` is special since it can be signed or unsigned depending on platform. Keep in mind regardless of its signedness, it is still considered a distinct type from both the `unsigned char` and `signed char` type.
%%ANKI
Basic
Is declaration `char` signed or unsigned?
Back: This is implementation-dependent.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1707493017239-->
END%%
**Narrow types** cannot be used directly in arithmetic. Instead they are first promoted to a wider type. On almost every system, this promotion will be to a `signed int` of the same value, regardless of the signedness of the narrow type itself.
%%ANKI
Basic
Why are narrow types named the way they are?
Back: They are considered to small to be used directly in arithmetic expressions.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121959-->
END%%
%%ANKI
Basic
Signed narrow types are usually promoted to what larger type?
Back: A `signed int`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121968-->
END%%
%%ANKI
Basic
Unsigned narrow types found are usually promoted to what larger type?
Back: A `signed int`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121972-->
END%%
### Unsigned
These correspond to nonnegative integer values.
| Name | Narrow | Rank |
| -------------------- | ------ | ---- |
| `bool` | Yes | 0 |
| `char` (maybe) | Yes | 1 |
| `unsigned char` | Yes | 1 |
| `unsighed short` | Yes | 2 |
| `unsigned int` | No | 3 |
| `unsigned long` | No | 4 |
| `unsigned long long` | No | 5 |
%%ANKI
Basic
Which basic unsigned type has the smallest rank?
Back: `bool`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121975-->
END%%
%%ANKI
Basic
Which unsigned type next succeeds `bool` in rank?
Back: `unsigned char` and (maybe) `char`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121979-->
END%%
%%ANKI
Basic
Which unsigned type next succeeds `unsigned char` in rank?
Back: `unsigned short`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121983-->
END%%
%%ANKI
Basic
Which unsigned type next succeeds `unsigned short` in rank?
Back: `unsigned int`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121987-->
END%%
%%ANKI
Basic
Which unsigned type next succeeds `unsigned int` in rank?
Back: `unsigned long`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121993-->
END%%
%%ANKI
Basic
Which unsigned type next succeeds `unsigned long` in rank?
Back: `unsigned long long`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859121999-->
END%%
%%ANKI
Basic
Which unsigned type next succeeds `unsigned long long` in rank?
Back: N/A.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122007-->
END%%
%%ANKI
Basic
Which unsigned narrow type has the highest rank?
Back: `unsigned short`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122015-->
END%%
%%ANKI
Basic
Which unsigned non-narrow type has the smallest rank?
Back: `unsigned int`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122023-->
END%%
### Signed
These correspond to possibly negative integer values.
| Name | Narrow | Rank |
| -------------------- | ------ | ---- |
| `char` (maybe) | Yes | 1 |
| `signed char` | Yes | 1 |
| `signed short` | Yes | 2 |
| `signed int` | No | 3 |
| `signed long` | No | 4 |
| `signed long long` | No | 5 |
| `float` | - | - |
| `double` | - | - |
| `long double` | - | - |
%%ANKI
Basic
Which basic signed type has the smallest rank?
Back: `signed char` and (maybe) `char`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122030-->
END%%
%%ANKI
Basic
Which signed type succeeds `signed char` in rank?
Back: `signed short`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122037-->
END%%
%%ANKI
Basic
Which signed type succeeds `signed short` in rank?
Back: `signed int`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122044-->
END%%
%%ANKI
Basic
Which signed type succeeds `signed int` in rank?
Back: `signed long`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122052-->
END%%
%%ANKI
Basic
Which signed type succeeds `signed long` in rank?
Back: `signed long long`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122059-->
END%%
%%ANKI
Basic
Which signed type succeeds `signed long long` in rank?
Back: N/A.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122066-->
END%%
%%ANKI
Basic
Which signed narrow type has the highest rank?
Back: `signed short`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122073-->
END%%
%%ANKI
Basic
Which signed non-narrow type has the smallest rank?
Back: `signed int`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1723859122080-->
END%%
### Literals
Negative integer literals are typed in a counterintuitive way. When the compiler sees a number of form `-X`, the type of `X` is determined *before* being negated. Promotion rules are as follows:
| Decimal | Oct/Hex |
| ----------- | -------------------- |
| `int` | `int` |
| `long` | `unsigned` |
| `long long` | `long` |
| `-` | `unsigned long` |
| `-` | `long long` |
| `-` | `unsigned long long` |
%%ANKI
Basic
How does the compiler process integer literal `-X`?
Back: By first determining the type of `X` and then negating the value.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820805-->
END%%
%%ANKI
Basic
What integer literals are guaranteed `signed`?
Back: Decimal integer constants.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820826-->
END%%
%%ANKI
Basic
How do we specify an octal integer literal?
Back: Prepend the literal with a `0`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1710673807992-->
END%%
%%ANKI
Basic
Why avoid negative octal integer literals?
Back: Depending on value, the resulting type may be `unsigned`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820829-->
END%%
%%ANKI
Basic
How do we specify a hexadecimal integer literal?
Back: Prepend the literal with a `0x` or `0X`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1710673807995-->
END%%
%%ANKI
Cloze
Octal literals are to {`0`} whereas hexadecimal literals are to {`0x`/`0X`}.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1710673807997-->
END%%
%%ANKI
Basic
How might C dangerously interpret a negative hexadecimal integer literal?
Back: Depending on the value, the resulting type may be `unsigned`.
Reference: Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820833-->
END%%
%%ANKI
Basic
Which header file contains `INT_MAX`?
Back: `<limits.h>`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708615249864-->
END%%
%%ANKI
Cloze
{`INT_MAX`} is to `signed` whereas {`UINT_MAX`} is to `unsigned`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820837-->
END%%
%%ANKI
Basic
How does `<limits.h>` define `INT_MIN`?
Back: As `(-INT_MAX - 1)`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820840-->
END%%
%%ANKI
Basic
*Why* is `INT_MIN` defined as `(-INT_MAX - 1)` instead of directly as e.g. `-2147483648`?
Back: Because `2147483648` (without `-`) would be sized as a non-`int` before being negated.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820843-->
END%%
%%ANKI
Cloze
`INT_MAX` is to {`<limits.h>`} whereas `INT32_MAX` is to {`<stdint.h>`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708615249873-->
END%%
%%ANKI
Basic
What suffix can be used to denote an `unsigned` integer literal?
Back: Case-insensitive `U`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708615249876-->
END%%
%%ANKI
Basic
What suffix can be used to denote a `long` integer literal?
Back: Case-insensitive `L`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820847-->
END%%
%%ANKI
Basic
What suffix can be used to denote a `long long` integer literal?
Back: Case-insensitive `LL`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820850-->
END%%
%%ANKI
Basic
What suffix can be used to denote an `unsigned long long` integer literal?
Back: Case-insensitive `ULL`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708631820856-->
END%%
%%ANKI
Basic
In what order does C cast size and "signedness"?
Back: C casts size then signedness.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608760-->
END%%
%%ANKI
Basic
In what order does C cast "signedness" and size?
Back: C casts size then signedness.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677626482-->
END%%
%%ANKI
Basic
Given `short sx`, cast `(unsigned) sx` is more explicitly written as what other sequence of casts?
Back: `(unsigned) (int) sx`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608762-->
END%%
%%ANKI
Basic
Given `short sx`, are the following two lines equivalent?
```c
(unsigned) sx
(unsigned) (int) sx
```
Back: Yes.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608764-->
END%%
%%ANKI
Basic
Given `short sx`, are the following two lines equivalent?
```c
(unsigned) sx
(unsigned) (unsigned short) sx
```
Back: No.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608766-->
END%%
%%ANKI
Basic
Given `short sx`, why is the following not an identity?
```c
(unsigned) sx = (unsigned) (unsigned short) sx
```
Back: `(unsigned) sx` casts size before "signedness".
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608767-->
END%%
%%ANKI
Basic
What does "signedness" of a variable refer to?
Back: Whether the variable was declared `signed` or `unsigned`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1714677608769-->
END%%
## Bibliography
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
* Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).