Questionnaire

$75\%$ of students are new to programming.

To C Beginners

From Beginners to Masters

Programming

De-programming

What is C?

C is a computer programming language (PL).

You communicate your ideas to computers via PLs.

What is C?

Programming is NOT (only) about languages.

Programming is not about C.

You learn C to express YOUR IDEAS.

How to Learn (1)?

How to Learn (2)?

"无他, 但手熟尔"

How to Learn (3)?

How many bugs have you ever produced?

C Programming:
A Modern Approach

C Primer Plus

K&R C Bible

K&R

Brian W. Kernighan (1942 ~)

Dennis M. Ritchie (1941 ~ 2011)

Examination and Scores

考勤
~~期中测试~~
~~期末笔试~~
期末机试 (30 分)
编程练习 (70 分)
奖励

编程练习: 每周基础训练 (40 分) + 学期项目 (30 分; 2 个)

Q&A

CLion

"你有你的选择, 而我选择 CLion"

Hello World (K&R C)

Hello World (Standard C)

#include <stdio.h>

int main() {
  printf("Hello World\n");
  return 0;
}

Brief History of C

You do not have to become a language lawyer.

Brief History of C

Turing Award (1983)

Game: Guess the Number

Guess the Number

Game: Guess the Number

Quote: Programming is Thinking, not Typing

You think. I will type it for you.

How to Obtain a Random Number?

How to Obtain a Random Number?

How to Obtain a Random Number?

$s \qquad f(s) \qquad f(f(s)) \qquad \ldots$

pseudo-random number sequence

How to Obtain a Random Number?

https://en.cppreference.com/w/c

Code Style

Braces

Tabs vs. Spaces

Code Style in CLion

Programming Style Guide

Google Style Guides

华为C语言编程指南.pdf

Secure C

How to Obtain a Random Number (Revisited)?

What is Next?

Variables and Types (int, double)
Math: computer arithmetic
Input/Ouput (I/O)

Branching: "if/else", "switch/case"
Looping: "while", "do/while", "for"
Jumps: "break", "continue", "goto"

Functions & Libraries

Keeping Programming

GitHub Classroom @ Bilibili

No Plagiarism!!!

前两次各扣 10 分, 第三次总分降为 60 分 $\;(\times\; 60\%)$

Resources

6735 99232 2021-C-PL

Resources

发布课件、资料、调查问卷等

Resources

problemoverflow.cn

Variables, Types, IO

Hengfeng Wei

hfwei@nju.edu.cn

Oct. 11, 2021

Overview

Variables (变量) Constants (常量)

Data Types (数据类型)

Operators (运算符) Expressions (表达式)

Assignment Statements (赋值语句)

I/O (Input/Output; 输入输出)

"Talk is Cheap. Show me the Code."

circle.c sphere.c mol.c admin.c

Circle

Given a radius ( $10$ ) of a circle,

to compute its circumference and area.

$L = 2\pi r$ $S = \pi r^2$

每个结果各占一行
小数点后保留两位

Declaration (声明)

int radius = 10;

Introduce a variable called radius.
You can use radius later.
The type of radius is int (integer).
radius is initialized (初始化) to 10.
You can assign (赋值) other values to radius.
radius refers to a location (&radius) in memory.

Definition (定义)

int radius = 10; is also a definition.

Any definitions are declarations.

~~All declarations are definitions~~ (at least for now).

Identifiers (标识符)

int radius = 10;

The name radius is an identifier.

made up of letters, numbers, and underscores
do not start with a number

Identifiers

Use meaningful identifiers
surface_area vs. surfaceArea

Operators and Expressions

double circumference = 2 * PI * radius;

Assignment Statements

double circumference = 0;

circumference = 2 * PI * radius;

Sphere

Given a radius ( $100$ ) of a sphere,

to compute its surface area and volume.

$A = 4 \pi r^2$ $V = \frac{4}{3} \pi r^3$

每个结果各占一行
小数点后保留四位
每个结果至少占 $15$ 字符, 左对齐
- _______________ : surface_area
- _______________ : volume

mol

$6$ 克氧气的物质的量是多少?

$Q = 6 / 32 \times 6.02 \times 10^{23}$

两种格式输出, 结果均使用科学计数法表示

第一行结果, 小数点后保留三位
第二行结果, 保留五位有效数字

Data Types

int ( $\approx \mathbb{Z}$ )
double ( $\approx \mathbb{R}$ )
char (Character; 字符)
C string (char array; 字符数组)

`int` $\approx \mathbb{Z}$

INT_MIN INT_MAX

printf("INT_MIN = %d \t INT_MAX = %d\n", INT_MIN, INT_MAX);

A (Naive) Administration System

Name (EN)
Gender (F/M)
Birthday (mm-dd-yyyy)
Weekday (Xyz.)

C
Music
Medicine
Mean (.d)
Standard Deviation (.dd)
Ranking ( $\%$ )

A (Naive) Administration System

每组信息占一行
各项信息使用 "TAB" 间隔
各项信息要遵循特定格式要求

罗大佑

Data Types: `char`

isdigit isalpha isalnum
islower isupper tolower toupper
isspace (including , \n, \t)

Data Types: `C string`

char first_name[] = "Tayu";

A C string is an array of characters.

'\0': terminating null character

'T', 'a', 'y', 'u', '\0'

char first_name[5] = "Tayu";

char first_name[10] = "Tayu";

~~char first_name[2] = "Tayu";~~

`printf`

int printf(const char *format, ...);

format: format string (格式串)
...: variable argument list (可变长参数列表)

`printf`

int printf(const char *format, ...);

The format string consists of

ordinary characters (not %)
conversion specifications (转换说明)
- each of which is introduced by %

`printf`

int printf(const char *format, ...);

Escape sequence (转义序列)

\n: Newline
\t: Horizontal Tab
\": Double quotation mark
\': Single quotation mark
\\: Backslash
\b: Backspace

`printf`

int printf(const char *format, ...);

%specifier	Argument	Output
%d (%i)	int	decimal ([-]dddd)
%f	double	decimal ([-]ddd.ddd)
%e (%E)	double	decimal ([-]d.ddde[+-]dd)
%g (%G)	double	%f or %e

`printf`

int printf(const char *format, ...);

%specifier	Argument	Output
%c	int	character
%s	pointer to a char array	string
%%		%

`printf`

"It is up to you to ensure that

the type of the actual argument

matches the type expected by conversion specifiers."

`printf`

%[flags][width][.precision]specifier

int printf(const char *format, ...);

flags
- -: left-justified (otherwise, right-justified)
- +: always begin with a plus or minus sign

`printf`

%[flags][width][.precision]specifier

int printf(const char *format, ...);

width
- minimum field width
- padded with spaces if it has fewer characters

`printf`

%[flags][width][.precision]specifier

int printf(const char *format, ...);

%d, %i: minimum number of digits
- expanded with leading zeros when needed
%f, %e, %E: number of digits after '.'
- default is $6$
%g, %G: maximum number of significant digits
%s: maximum number of characters

`scanf`

int scanf(const char *format, ...);

format: format string (格式串)
...: variable argument list (可变长参数列表)

`scanf`

int scanf(const char *format, ...);

The format string consists of

white-space characters
ordinary characters
- neither % nor white-spaces
conversion specifications
- each of which is introduced by %

`scanf`

int scanf(const char *format, ...);

Scan the input stream from left to right
Identify expected items as long as possible

`scanf`

int scanf(const char *format, ...);

%specifier	Matched Item	Argument
%d	skip white-spaces; matches an `int`	pointer to `int`
%le, %lf, %lg	skip white-spaces; matches a `double`	pointer to `double`
%e, %f, %g	skip white-spaces; matches a `float`	pointer to `float`

`scanf`

%specifier	Matched Item	Argument
%c	a character	pointer to a `char`
%s	a sequence of non-white-spaces	pointer to a `char` array
%[abc]	scanlist	pointer to a `char` array
%[^abc]	not in scanlist	pointer to a `char` array
%%	%

`scanf`

%[ $\star$ ][width]specifier

int scanf(const char *format, ...);

$\star$ : assignment-suppressing
width: maximum field width

`scanf`

"It is up to you to ensure that

the type of each actual argument pointer

matches the type expected by conversion specifiers."

References

printf @ cppreference

scanf @ cppreference

References

Do not use scanf.

Use $\dots$ instead.

If, For, Array

Hengfeng Wei

hfwei@nju.edu.cn

Oct. 18, 2021

Review

Variables Constants Data Types

Operators Expressions Assignment Statements

I/O (Input/Output)

Constants

int: 42
double: 3.14
char: 'c'
string: "Hello World"

Literal constants (字面常量)

const double PI = 3.14159;

PI is still a variable.

Overview

If Statement (If 语句)

For Statement (For 语句)

Logical Expressions (逻辑表达式)

Array (数组)

"Talk is Cheap. Show me the Code."

min leap

sum.c min.c

Min

Min of Two

Given two integers $a$ and $b$ ,

to compute their minimum.

$\mathit{min} = \min\{a, b\}$

`if`

The else part is optional.

`if`

Multiple declarations and statements surrounded by {}

Always Use `{}`!

Relational Operators (关系运算符)

>=
<=
>
<
== (equal to)
!= (not equal to)

Relational Expressions (关系表达式)

Relational expressions have values 0 (false) or 1 (true).

In C, non-zero numbers are treated as 1 (true).

`?:`

min = a >= b ? b : a;

Conditional Expression (条件表达式)

Ternary Operator (三目运算符)

Do Not Use it Too Much!

Min of Three

Given three integers $a$ , $b$ , and $c$ ,

to compute their minimum.

$\mathit{min} = \min\{a, b, c\}$

Nested `if`

Min of a Set of Numbers

Given a set $A$ of integers,

to compute their minimum.

$\mathit{min} = \min A$

Leap Year

Leap Year (1): Nested `if`

Leap Year (2): Nested `if`

Leap Year (3): `else-if`

Leap Year (4): The Ultimate Version

A year is a leap year if

it is divisible by 4 but not by 100,
except that years divisible by 400 are leap years.

Logical Operators (逻辑运算符)

Logical Expressions (逻辑表达式)

Logical expressions have values 0 (false) or 1 (true).

Short-circuit Evaluation

year = 25
year = 80

Sum

Given an integer $n \ge 0$ , to compute $\sum\limits_{i = 1}^{n} i$ .

Increment/Decrement Operators (`++`, `--`)

i++
- increment i after its value has been used
++i
- increment i before its value is used

Increment/Decrement Operators (`++`, `--`)

i = 2;

j = i * i++;

Undefined Behavior (未定义行为)

For Statement

Min of a Set of Numbers

Given a set $A$ of integers,

to compute their minimum.

$\mathit{min} = \min A$

`#define NUM 5`

Symbolic Constants (符号常量)

#define is a pre-processing directive (预处理指令).

int numbers[NUM] = {0}; has a constant size.

NUM is known at compiler time.

Array Initializer

int numbers[NUM] = {0};

int numbers[NUM] = {1};
- {1, 0, 0, 0, 0}
int numbers[] = {0};
- {0}
int numbers[NUM] = {[2] = 1};
- {0, 0, 1, 0, 0}
- See Section 8.1.3

Array Initializer

int numbers[NUM] = {0};

~~int numbers[NUM] = {};~~
- Forbidden in C99 (Unfortunately)
- Allowed by GCC by default (Unfortunately)
~~int numbers[NUM];~~
- May contain garbage values
~~int numbers[];~~
- You must specify the size so that the compiler can allocate memory for it.

Array Members

[]: subscript operator (下标运算符)

For a While

Hengfeng Wei

hfwei@nju.edu.cn

Oct. 25, 2021

Review

If Statement

For Statement

Logical Expressions

Array

Overview

For Statement (More Examples)

While (Do-While) Statement

`break` Statement

"Talk is Cheap. Show me the Code."

Stars Pyramid

stars.c

Prime Numbers

prime.c primes.c

Selection Sort

selection-sort.c

Palindrome

palindrome.c

Binary Search

binary-search.c

Number of Digits

digits-while.c digits-do-while.c

Counting

counting-if.c counting-switch.c

Loops

Hengfeng Wei

hfwei@nju.edu.cn

Nov. 01, 2021

No Plagiarism!!!

第一次作业抄袭现象触目惊心

助教们敦促蚂老师召开了紧急磋商会议

会上大家对作业进行了反思, 并制定了严厉的抄袭处罚措施

No Plagiarism!!!

当次作业计 $0$ 分

前两次抄袭总评各扣 $10$ 分

第三次抄袭总评直接判为不及格 $\;(\times\; 60\%)$

No Plagiarism!!!

助教与第一次作业(疑似)抄袭的同学进行了亲切友好的交谈

口头警告, 算作一次抄袭记录, 不作总评扣分处理

Review

For Statement (More Examples)

While (Do-While) Statement

`break`

Overview

Loops (More Examples)

Multidimensional Arrays (多维数组)

`continue, goto`

"Talk is Cheap. Show me the Code."

Merge

merge.c

Bubble Sort

bubble-sort.c

Conway's Game of Life

John Horton Conway ( $1937 \sim 2020$ )

playgameoflife.com

Conway's Game of Life

Any live cell with two or three live neighbours survives.
All other live cells die in the next generation.

Any dead cell with three live neighbours becomes a live cell.
All other dead cells stay dead.

Conway's Game of Life @ wiki

Conway's Game of Life

game-of-life.c

Counting

counting-if.c counting-switch.c

Jump Statements

break continue goto

common.c continue.c

Function

Hengfeng Wei

hfwei@nju.edu.cn

Nov. 08, 2021

Review

Loops (More Examples)

Multidimensional Arrays

Overview

Functions

"Talk is Cheap. Show me the Code."

Re-writing Programs using Functions

Recursion

Hengfeng Wei

hfwei@nju.edu.cn

Nov. 15, 2021

Review

Functions

Function Declaration
Function Definition
Arrays as Parameters
Pass by Value

Overview

Recursive Functions (Recursion)

A function that calls (调用) itself.

Recursion

Thinking Recursively

It is a looooooog way to go to master recursion!!!

Recursion: Systems Implementation

Programs run in memory (内存; 記憶體).

Memory = Stack (栈区) + Heap (堆区) + $\cdots$

Each function call has its own stack frame (栈帧).

Stack grows/shrinks with function calls and returns.

Recursion: Systems Implementation

Visualization of Function Calls @ C Tutor

Recursion: Mathematical Induction

Base Case (基础情况)

Inductive Step (归纳步骤)

"Talk is Cheap. Show me the Code."

Min

min-re.c

Sum

sum-re.c

Fibonacci Sequence

$0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, \ldots$

$F_{0} = 0$
$F_{1} = 1$
$F_{n} = F(n - 1) + F(n - 2) \qquad (n > 1)$

fib-re.c fib-array.c fib-iter.c

Greatest Common Divisor

$a > b \implies \text{gcd}(a, b) = \text{gcd}(a - b, b)$
$a < b \implies \text{gcd}(a, b) = \text{gcd}(a, b - a)$

gcd-euclid-re.c gcd-euclid-iter.c

Greatest Common Divisor

$\text{gcd}(a, b) = \text{gcd}(b, a \;\%\; b)$

gcd-euclidean-re.c gcd-euclidean-iter.c

Binary Search

bsearch-re.c

Recursion; Data Types

Hengfeng Wei

hfwei@nju.edu.cn

Nov. 22, 2021

Review

Recursion

A function that calls itself.

Recursion

Thinking Recursively

Overview

Recursion (More Examples)

Data Types

static

"Talk is Cheap. Show me the Code."

Binary Search

bsearch-re.c

Merge Sort

merge-sort.c

Data Types

The type of a variable determines

the set of values it may take on and

what operations can be performed on them.

int double char

Integral Types

Signed (有符号数)

short int
int
long
long long

Unsigned (无符号数)

bool (stdbool.h)
unsigned short int
unsigned int
unsigned long
unsigned long long

char (unsigned/signed)

Overflow (溢出)

有符号整数运算中发生溢出, 程序的行为是未定义的。
无符号整数运算中发生溢出, 程序的行为是有定义的。

Integral Promotion (整型提升)

定义初始化
赋值操作
参数传递
函数返回值

Integral Promotion (整型提升)

"Arithmetic operators do not accept types smaller than int as arguments, and integral promotions are automatically applied."

Floating-point Numbers

float y = 5.0F
- %f
- %f
double x = 5.0
- %lf
- %f
long double z = 5.0L
- %Lf
- %Lf

Floating-point Numbers

Floating-point Arithmetic

"Floating-point Arithmetic is Hard."

Floating-point Arithmetic

float.h (Section 23.1)

Floating-point Arithmetic

Overflow (上溢)

Underflow (下溢)

Significance Loss (精度丢失)

significance.c

Floating-point Arithmetic

"Many applications don't need floating-point arithmetic at all."

Use math.h (Section 23.3) whenever possible.

C 语言安全编码标准

整型数安全编码标准 (INT)

使用正确的整数类型

确保无符号整数运算不产生回绕

确保有符号整数运算不造成溢出

确保除法与余数运算不造成除0错误

确保整数转换不会造成数据丢失或者错误解释

浮点数安全编码标准 (FLP)

不要使用浮点数变量作为循环计数器

避免或者检测数学函数中的定义域与值域错误

确保浮点数转换在新类型的范围中

References

Pointers

Hengfeng Wei

hfwei@nju.edu.cn

Nov. 29, 2021

Overview

Pointers and Arrays Pointers and C Strings

Overview

Pointers

"A pointer is a variable that

contains the address of a variable."

"Talk is Cheap. Show me the Code."

Variables Revisited

int radius = 10;

radius refers to a location (&radius) in memory.

&: Address-of Operator ("取地址"运算符)

printf("%p\n", &radius);

Pointers

int *ptr_radius = &radius;

The type of ptr_radius is "pointer to int".

Variables Revisited

double circumference = 2 * 3.14 * radius;

radius = 20;

A variable behaves as an lvalue or a rvalue.

左值右值

Pointers

int *ptr_radius = &radius;

*ptr_radius behaves just like radius does.
- *: Indirection/Dereferencing ("间接寻址/解引用"运算符)

double circumference = 2 * 3.14 * (*ptr_radius);

*ptr_radius = 20;

Pointers

int *ptr_radius = &radius;

ptr_radius is also a variable.

Swap Numbers

selection-sort.c

Min and Max

Compute both the min and the max

of an array of integers.

min-max.c

scanf.c

Dynamic Memory Management

int *numbers = malloc(len * sizeof *numbers);

void *malloc(size_t size);

void free(void *ptr);

selection-sort.c

Dynamic Memory Management

stdlib.h ~~malloc.h~~

Pointers and Arrays

The name of an array is a synonym for the address of its first element.

numbers[i] *(numbers + i) ~~i[numbers]~~

&numbers[i] numbers + i

But an array name is not a variable.
- ~~numbers++~~

Pointers and C Strings

char msg[20] = "Hello World!";

char *msg = "Hello World!";

strlen.c

strlen strlen_s

Pointers and C Strings

strcmp.c

strcmp

strncmp

Pointers and C Strings

strcpy.c

strcpy strcpy_s

strncpy strncpy_s

Return Pointers from Functions

Do not return pointers to

local variables in functions!!!

References

Chapter 14: string.h

Pointer Arrays

selection-sort-strings.c

Pointers (More)

Hengfeng Wei

hfwei@nju.edu.cn

Dec. 06, 2021

Review

Pointers and Arrays Pointers and C Strings

Overview

string.h

Pointer Arrays Pointers and 2D Arrays

Function Pointers

"Talk is Cheap. Show me the Code."

Pointers; Structures

Hengfeng Wei

hfwei@nju.edu.cn

Dec. 13, 2021

Review

string.h

Pointer Arrays Pointers and 2D Arrays

Overview

Program Arguments Function Pointer

struct union enum

"Talk is Cheap. Show me the Code."

Linked Lists

Hengfeng Wei

hfwei@nju.edu.cn

Dec. 20, 2021

Review and Overview

Program Arguments Function Pointer

struct union enum

Overview: Linked Lists

"Talk is Cheap. Show me the Code."

`struct`

musician.c

Linked Lists

Singly Linked List

Doubly Linked List

Linked Lists

Circular Linked List

Introducing C

Hengfeng Wei (魏恒峰)

hfwei@nju.edu.cn