Review of Programming (C)

Key Terms

Term	中文	Definition / Notes
IPO (Input–Process–Output)	输入–处理–输出	A conceptual model describing how a computer system receives data, manipulates it according to programmed instructions, and produces results.
compiler	编译器	A tool (e.g., GCC, or MSVC) that translates human-readable C source code into machine code that the CPU can execute directly.
preprocessor directive	预处理器指令	An instruction beginning with # that is processed before compilation proper; it typically inserts header file contents into the source, e.g., #include.
header file	头文件	A file containing declarations of library functions, e.g., stdio.h; included via #include so the compiler knows how to handle calls such as printf() and scanf().
main() function	主函数	The designated entry point of every C programme; execution begins at the first statement inside main().
printf()	格式化输出函数	A standard library function declared in <stdio.h> used to write formatted text to standard output (the console).
scanf()	格式化输入函数	A standard library function declared in <stdio.h> used to read formatted input from standard input (the keyboard).
format specifier	格式说明符	A placeholder within a format string (e.g., %d for integers, %f for floating-point numbers, %s for strings) that indicates the type of data to be printed or read.
source file	源文件	A plain-text file with a .c extension containing C source code.
executable	可执行文件	The binary file produced by the compiler, which can be run directly by the operating system (OS).
variable	变量	A named storage location in memory that holds a value which may change during programme execution. Every variable has a type, a name, an address, and a value.
constant	常量	A value that cannot be altered after it is defined. May be established via #define (preprocessor macro) or const (typed, read-only variable).
literal	字面量	A fixed value written directly in the source code, such as 42 (integer literal), 3.14 (floating-point literal), 'A' (character literal), or "hello" (string literal).
identifier	标识符	The name given to a variable, function, or other user-defined entity. Must begin with a letter or underscore, followed by letters, digits, or underscores. Case-sensitive.
keyword (reserved word)	关键字（保留字）	A word with a predefined meaning in C (e.g., int, return, while) that cannot be used as an identifier.
data type	数据类型	A classification that specifies the kind of value a variable can hold and the amount of memory allocated for it, e.g., int, float, double, char.
type modifier	类型修饰符	A qualifier that alters the size or sign of a base type: signed, unsigned, short, long.
declaration	声明	The act of informing the compiler of a variable's name and type, e.g., int age;. Memory is reserved but the value is indeterminate.
assignment	赋值	The act of storing a value in a previously declared variable, e.g., age = 19;.
initialisation	初始化	Declaring and assigning a value in a single statement, e.g., int age = 19;.
operator precedence	运算符优先级	The hierarchy that determines the order in which operators are evaluated within an expression.
associativity	结合性	The direction (left-to-right or right-to-left) in which operators of equal precedence are evaluated.
implicit conversion	隐式类型转换	An automatic type conversion performed by the compiler when operands of different types appear in the same expression (e.g., int promoted to float).
explicit casting	显式类型转换（强制类型转换）	A programmer-directed type conversion using the cast operator, e.g., (int)3.14.
ASCII	美国信息交换标准代码	American Standard Code for Information Interchange — a character encoding in which each character is represented by a numeric value, e.g., 'A' = 65.
sizeof	sizeof 运算符	A compile-time operator that returns the size, in bytes, of a type or variable.
relational operator	关系运算符	Returns 1 (true) or 0 (false). Do not confuse with arithmetic operators.
logical operator	逻辑运算符	&&, `
selection structure	选择结构	One of the three fundamental control structures (sequence, selection, repetition).
condition / Boolean expression	条件 / 布尔表达式	Any expression whose value is interpreted as true (non-zero) or false (zero).
if statement	if 语句	Executes a block only when the condition is true.
if-else statement	if-else 语句	Two-branch selection: one block for true, another for false.
if-else ladder	if-else 阶梯	Chain of else if clauses testing conditions top-to-bottom.
nested if	嵌套 if	An if (or if-else) placed inside another if or else block.
switch statement	switch 语句	Multi-way branch on an integer or character value.
fall-through	穿透	Default switch behaviour when break is omitted; execution continues into the next case.
short-circuit evaluation	短路求值	&& stops if the left operand is false; `
precedence	优先级	The order in which operators are evaluated, e.g., arithmetic > relational > logical > assignment.
associativity	结合性	Direction of evaluation for operators of equal precedence (left-to-right or right-to-left).
repetition structure / loop	循环结构	The third fundamental control structure; repeats a block while a condition holds.
entry-controlled loop	入口控制循环	Condition tested before the body executes (while, for). Body may execute zero times.
exit-controlled loop	出口控制循环	Condition tested after the body executes (do-while). Body always executes at least once.
while loop	while 循环	Entry-controlled; most general form of loop.
do-while loop	do-while 循环	Exit-controlled; guarantees at least one execution of the body.
for loop	for 循环	Entry-controlled; bundles initialisation, condition, and modification into one header.
counter-controlled loop	计数器控制循环	Iteration count is known in advance, e.g., repeat 10 times.
event-controlled / sentinel loop	事件 / 哨兵控制循环	Iteration ends when a special sentinel value is encountered; count is unknown in advance.
sentinel value	哨兵值	A marker value distinct from valid data that signals the end of input, e.g., −1.
compound assignment operator	复合赋值运算符	+=, -=, *=, /=, %= — shorthand for var = var op expr.
increment / decrement operator	自增 / 自减运算符	++ / --. Prefix form modifies before use; postfix form modifies after use.
nested loop	嵌套循环	A loop placed inside the body of another loop; the inner loop completes all iterations per outer iteration.
break	break 语句	Immediately exits the innermost enclosing loop (or switch).
continue	continue 语句	Skips the remainder of the current iteration and jumps to the next condition check (or modification step in for).
infinite loop	无限循环	A loop whose condition never becomes false (e.g., while (1)); must contain a break or external termination.
parameterisation	参数化	Replacing hard-coded constants with variables so that a programme adapts to different inputs without rewriting.
array	数组	A fixed-size, contiguous block of elements of the same type.
index (subscript)	下标/索引	Starts from 0 in C, not 1. arr[0] is the first element if the array is declared as arr.
initialiser list	初始化列表	Brace-enclosed values, e.g. {1, 2, 3}. Partial initialisation zero-fills the remainder.
contiguous memory	连续内存	Array elements are stored adjacently; address of element i = base + i × element size.
null terminator	空字符 / 终止符	'\0' marks the end of a C string; a char array of n visible characters requires n + 1 bytes.
C string	C字符串	A char array terminated by '\0'; not a first-class type but a convention.
fgets()	–	Reads up to size − 1 characters including spaces; safer than gets(), which is deprecated.
two-dimensional array	二维数组	An array of arrays; stored in row-major order in memory.
row-major order	行优先存储	Elements of the same row are contiguous in memory.
bubble sort	冒泡排序	An O(n²) comparison-based sorting algorithm that repeatedly swaps adjacent elements.
sentinel value	哨兵值	A special value (e.g. −1) used to signal the end of input rather than specifying a fixed count.
function declaration (prototype)	函数声明（原型）	Tells the compiler about name, return type, and parameter types; ends with ;; no body.
function definition	函数定义	Contains the actual body (implementation). Must match its prototype.
function call (invocation)	函数调用	The point in code where execution transfers to the function.
parameter (formal parameter)	形式参数 / 型参	The variable names listed in the function header.
argument (actual parameter)	实际参数 / 值参	The concrete values or expressions supplied at the call site. Easily confused with parameter.
return type	返回类型	The data type of the value the function hands back; void if none.
pass by value	值传递	The default in C for scalar types—a copy is passed.
pass by reference	引用传递	In C, achieved via pointers. Arrays are effectively passed by reference.
stack frame	栈帧	A block of memory on the call stack holding a function's local variables, parameters, and return address.
recursion	递归	A function that calls itself; must have a base case to terminate.
base case	基线条件	The condition under which a recursive function stops calling itself.
scope	作用域	The region of source code in which a variable is visible.
local variable	局部变量	Declared inside a function or block; visible only there.
global variable	全局变量	Declared outside all functions; visible to every function that follows its declaration.
library function	库函数	Pre-built functions provided by the C Standard Library, e.g. printf(), sqrt().
user-defined function	用户自定义函数	Functions written by the programmer.
modular design	模块化设计	Structuring a programme as a collection of independent, well-defined modules (functions).
pointer	指针	A variable whose value is a memory address.
address-of operator &	取地址运算符	Yields the address of its operand; do not confuse with the bitwise AND &.
dereference operator *	解引用运算符	Accesses the value stored at the address held by a pointer; same symbol as the declaration *, but used in a different syntactic position.
NULL pointer	空指针	A pointer that points to nothing; defined in <stdio.h> and <stdlib.h>. Dereferencing NULL causes undefined behaviour.
pointer arithmetic	指针算术	Adding or subtracting an integer to/from a pointer; the offset is automatically scaled by sizeof the pointed-to type.
malloc() / free()	动态内存分配 / 释放	Library functions in <stdlib.h> for heap allocation. Always check the return value of malloc() and always call free() when the memory is no longer needed.
pointer to pointer	二级指针	A pointer that stores the address of another pointer, e.g. int **pp;.
function pointer	函数指针	A pointer that stores the address of a function; enables indirect (dynamic) function calls. Syntax: return_type (*name)(param_list);.
dangling pointer	悬空指针	A pointer that refers to memory that has been freed or has gone out of scope; dereferencing it is undefined behaviour.
bit	比特（位）	The smallest unit of data: 0 or 1.
byte	字节	= 8 bits.
Most Significant Bit (MSB)	最高有效位	The leftmost bit; in a signed integer it is the sign bit.
Least Significant Bit (LSB)	最低有效位	The rightmost bit; determines whether a number is odd or even.
numeral system (radix/base)	进制（基数）	A writing system for numbers; common bases are 2, 8, 10, 16.
binary (Base-2)	二进制	Digits 0–1. C prefix: 0b (GCC/Clang extension) or no standard prefix.
octal (Base-8)	八进制	Digits 0–7. C prefix: 0 (leading zero).
hexadecimal (Base-16)	十六进制	Digits 0–9, A–F. C prefix: 0x or 0X.
two's complement	补码	The standard signed-integer representation: invert all bits and add 1.
bitwise AND (&)	按位与	Result bit is 1 only when both operand bits are 1.
bitwise OR (`	`)	按位或
bitwise XOR (^)	按位异或	Result bit is 1 when the operand bits differ. Easily confused with exponentiation (which C does not have).
bitwise NOT (~)	按位取反	Flips every bit; unary operator.
left shift (<<)	左移	Shifts bits leftward, filling with 0 on the right. Equivalent to multiplication by 2ⁿ.
right shift (>>)	右移	Shifts bits rightward. For unsigned types, fills with 0 (logical shift); for signed types, typically fills with the sign bit (arithmetic shift — implementation-defined).
bit mask	位掩码	A value used with a bitwise operator to select, set, clear, or toggle specific bits.
set a bit	置位	Force a bit to 1 using OR with a mask.
clear a bit	清位	Force a bit to 0 using AND with the complement of a mask.
toggle a bit	翻转位	Flip a bit using XOR with a mask.
struct	结构体	A user-defined composite type that groups variables of different types under one name. Members are accessed with . (by value) or -> (by pointer).
typedef	类型别名	Creates an alias for an existing type; commonly used with struct to avoid repeating the struct keyword.
union	联合体	Like a struct, but all members share the same memory; only one member is valid at any time. The size of a union equals the size of its largest member.
enum	枚举	Defines a set of named integer constants; by default values start at 0 and increment by 1, but may be set explicitly.
file stream	文件流	An abstraction provided by <stdio.h> for sequential reading or writing of data; represented by the FILE * type.
fopen() / fclose()	打开 / 关闭文件	fopen(path, mode) returns a FILE * (or NULL on failure); fclose(fp) flushes the buffer and releases the resource.
text mode	文本模式	Human-readable characters; modes "r", "w", "a", etc. Newline translation may occur on some platforms.
binary mode	二进制模式	Raw bytes preserving the exact memory layout; modes "rb", "wb", "ab", etc. Essential for non-text data such as images, audio, or struct records.
fprintf() / fscanf()	格式化文件写 / 读	Formatted I/O analogous to printf() / scanf(), but operating on a file stream rather than stdout / stdin.
fwrite() / fread()	二进制写 / 读	Transfer raw blocks of bytes between memory and a file; parameters are: data pointer, element size, element count, stream.
perror()	打印系统错误	Prints a user-supplied prefix followed by a colon and the system error message corresponding to the current value of errno.
EOF	文件结束标志	A macro (typically −1) returned by I/O functions to signal that the end of the file has been reached or that an error occurred.
argc / argv	命令行参数	argc is the count of command-line tokens (including the programme name); argv is an array of C strings containing those tokens.

Reserved Keywords

The following identifiers are reserved and may not be used as variable or function names. Keywords marked with a standard version were introduced in that revision of the language.

auto, break, case, char, const, continue, default, do, double, else, enum, extern, float, for, goto, if, inline (C99), int, long, register, restrict (C99), return, short, signed, sizeof, static, struct, switch, typedef, union, unsigned, void, volatile, while.

C Operator Precedence

The following table lists the precedence and associativity of C operators. Operators are listed top to bottom, in descending precedence.

See details here.

Precedence	Operator	Description	Associativity
1	++ --	Suffix/postfix increment and decrement	L-R
	()	Function call
	[]	Array subscripting
	.	Structure and union member access
	->	Structure and union member access through pointer
	(*type*){*list*}	Compound literal (C99)
2	++ --	Prefix increment and decrement	R-L
	+ -	Unary plus and minus
	! ~	Logical NOT and bitwise NOT
	(*type*)	Cast
	*	Indirection (dereference)
	&	Address-of
	sizeof	Size-of
	_Alignof	Alignment requirement (C11)
3	* / %	Multiplication, division, and remainder	L-R
4	+ -	Addition and subtraction
5	<< >>	Bitwise left shift and right shift
6	< <=	For relational operators < and ≤ respectively
	> >=	For relational operators > and ≥ respectively
7	== !=	For relational = and ≠ respectively
8	&	Bitwise AND
9	^	Bitwise XOR (exclusive or)
10	|	Bitwise OR (inclusive or)
11	&&	Logical AND
12	||	Logical OR
13	?:	Ternary conditional	R-L
14	=	Simple assignment
	+= -=	Assignment by sum and difference
	*= /= %=	Assignment by product, quotient, and remainder
	<<= >>=	Assignment by bitwise left shift and right shift
	&= ^= |=	Assignment by bitwise AND, XOR, and OR
15	,	Comma	L-R

ASCII Printable Characters

DEC	OCT	HEX	BIN	Symbol	Description
32	40	20	100000	SP	Space
33	41	21	100001	!	Exclamation mark
34	42	22	100010	"	Double quotes (or speech marks)
35	43	23	100011	#	Number sign
36	44	24	100100	$	Dollar
37	45	25	100101	%	Per cent sign
38	46	26	100110	&	Ampersand
39	47	27	100111	'	Single quote
40	50	28	101000	(	Open parenthesis (or open bracket)
41	51	29	101001	)	Close parenthesis (or close bracket)
42	52	2A	101010	*	Asterisk
43	53	2B	101011	+	Plus
44	54	2C	101100	,	Comma
45	55	2D	101101	-	Hyphen-minus
46	56	2E	101110	.	Period, dot or full stop
47	57	2F	101111	/	Slash or divide
48	60	30	110000	0	Zero
49	61	31	110001	1	One
50	62	32	110010	2	Two
51	63	33	110011	3	Three
52	64	34	110100	4	Four
53	65	35	110101	5	Five
54	66	36	110110	6	Six
55	67	37	110111	7	Seven
56	70	38	111000	8	Eight
57	71	39	111001	9	Nine
58	72	3A	111010	:	Colon
59	73	3B	111011	;	Semicolon
60	74	3C	111100	<	Less than (or open angled bracket)
61	75	3D	111101	=	Equals
62	76	3E	111110	>	Greater than (or close angled bracket)
63	77	3F	111111	?	Question mark
64	100	40	1000000	@	At sign
65	101	41	1000001	A	Uppercase A
66	102	42	1000010	B	Uppercase B
67	103	43	1000011	C	Uppercase C
68	104	44	1000100	D	Uppercase D
69	105	45	1000101	E	Uppercase E
70	106	46	1000110	F	Uppercase F
71	107	47	1000111	G	Uppercase G
72	110	48	1001000	H	Uppercase H
73	111	49	1001001	I	Uppercase I
74	112	4A	1001010	J	Uppercase J
75	113	4B	1001011	K	Uppercase K
76	114	4C	1001100	L	Uppercase L
77	115	4D	1001101	M	Uppercase M
78	116	4E	1001110	N	Uppercase N
79	117	4F	1001111	O	Uppercase O
80	120	50	1010000	P	Uppercase P
81	121	51	1010001	Q	Uppercase Q
82	122	52	1010010	R	Uppercase R
83	123	53	1010011	S	Uppercase S
84	124	54	1010100	T	Uppercase T
85	125	55	1010101	U	Uppercase U
86	126	56	1010110	V	Uppercase V
87	127	57	1010111	W	Uppercase W
88	130	58	1011000	X	Uppercase X
89	131	59	1011001	Y	Uppercase Y
90	132	5A	1011010	Z	Uppercase Z
91	133	5B	1011011	[	Opening bracket
92	134	5C	1011100	\	Backslash
93	135	5D	1011101	]	Closing bracket
94	136	5E	1011110	^	Caret - circumflex
95	137	5F	1011111	_	Underscore
96	140	60	1100000	`	Grave accent
97	141	61	1100001	a	Lowercase a
98	142	62	1100010	b	Lowercase b
99	143	63	1100011	c	Lowercase c
100	144	64	1100100	d	Lowercase d
101	145	65	1100101	e	Lowercase e
102	146	66	1100110	f	Lowercase f
103	147	67	1100111	g	Lowercase g
104	150	68	1101000	h	Lowercase h
105	151	69	1101001	i	Lowercase i
106	152	6A	1101010	j	Lowercase j
107	153	6B	1101011	k	Lowercase k
108	154	6C	1101100	l	Lowercase l
109	155	6D	1101101	m	Lowercase m
110	156	6E	1101110	n	Lowercase n
111	157	6F	1101111	o	Lowercase o
112	160	70	1110000	p	Lowercase p
113	161	71	1110001	q	Lowercase q
114	162	72	1110010	r	Lowercase r
115	163	73	1110011	s	Lowercase s
116	164	74	1110100	t	Lowercase t
117	165	75	1110101	u	Lowercase u
118	166	76	1110110	v	Lowercase v
119	167	77	1110111	w	Lowercase w
120	170	78	1111000	x	Lowercase x
121	171	79	1111001	y	Lowercase y
122	172	7A	1111010	z	Lowercase z
123	173	7B	1111011	{	Opening brace
124	174	7C	1111100	|	Vertical bar
125	175	7D	1111101	}	Closing brace
126	176	7E	1111110	~	Equivalency sign - tilde
127	177	7F	1111111	DEL	Delete