斯坦福C语言基础教程：EssentialC速览

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"EssentialC - Nick Parlante的C语言教程" 这篇文档是Nick Parlante编写的C语言基础教程，旨在快速概括C语言的所有基本特性。它适用于作为复习材料或者为那些有其他编程语言背景的学习者提供参考。教程涵盖了一系列主题，包括： 1. 变量：在C语言中，变量是用来存储数据的容器。你需要声明变量的类型，如int（整型）、char（字符型）等，然后给它们分配值。 2. 类型：C语言支持多种基本类型，如整型(int)、浮点型(float和double)。浮点型用于处理小数，而整型则处理无小数部分的数值。 3. 数据提升与截断：在不同类型之间进行运算时，会发生数据提升（例如，char到int），而在赋值或转换过程中，可能会发生数据截断，即丢失超出目标类型范围的部分。 4. 运算符：C语言有各种运算符，如算术运算符(+、-、*、/、%)、比较运算符(==、!=、<、>、<=、>=)和逻辑运算符(&&、||、!)。 5. 控制结构：包括if条件语句、while循环、for循环，这些是控制程序流程的关键工具。 6. 函数：函数是C语言中可重用代码的模块，可以接受参数并返回值。函数分为值参数和引用参数，前者传递副本，后者传递实际变量的引用。 7. 结构体(struct)：结构体允许你将多个不同类型的变量组合成一个单一的实体，方便处理复杂的数据结构。 8. 指针：指针是C语言的强项，它存储了内存地址，让你能够直接操作内存中的数据。指针与数组有许多相似之处，但指针可以动态改变所指向的内存位置。 9. 数组：数组是一系列相同类型元素的集合，可以通过索引来访问其成员。 10. 预处理器：预处理器在编译阶段处理源代码，主要负责宏定义(#define)和包含文件(#include)。 11. 标准C库函数：C语言提供了一套标准库函数，如数学运算的math.h库，输入输出的stdio.h库等，它们极大地扩展了C语言的功能。这个教程的最新版本可在Stanford CSEducation Library的网址http://cslibrary.stanford.edu/101/找到。作者鼓励读者分享和使用这份文档，以增进对C语言的理解。通过学习这篇教程，你可以掌握C语言的基础，并为进一步深入学习C语言和理解计算机科学的基本原理打下坚实基础。

var-- decrement "post" variant

--var decrement "pre" variant

int i = 42;

i++; // increment on i

// i is now 43

i--; // decrement on i

// i is now 42

Pre and Post Variations

The Pre/Post variation has to do with nesting a variable with the increment or decrement

operator inside an expression -- should the entire expression represent the value of the

variable before or after the change? I never use the operators in this way (see below), but

an example looks like...

int i = 42;

int j;

j = (i++ + 10);

// i is now 43

// j is now 52 (NOT 53)

j = (++i + 10)

// i is now 44

// j is now 54

C Programming Cleverness and Ego Issues

Relying on the difference between the pre and post variations of these operators is a

classic area of C programmer ego showmanship. The syntax is a little tricky. It makes the

code a little shorter. These qualities drive some C programmers to show off how clever

they are. C invites this sort of thing since the language has many areas (this is just one

example) where the programmer can get a complex effect using a code which is short and

dense.

If I want j to depend on i's value before the increment, I write...

j = (i + 10);

i++;

Or if I want to j to use the value after the increment, I write...

i++;

j = (i + 10);

Now then, isn't that nicer? (editorial) Build programs that do something cool rather than

programs which flex the language's syntax. Syntax -- who cares?

Relational Operators

These operate on integer or floating point values and return a 0 or 1 boolean value.

== Equal

!= Not Equal

> Greater Than

< Less Than

>= Greater or Equal

<= Less or Equal

To see if x equals three, write something like:

if (x == 3) ...

Pitfall = ==

An absolutely classic pitfall is to write assignment (=) when you mean comparison (==).

This would not be such a problem, except the incorrect assignment version compiles fine

because the compiler assumes you mean to use the value returned by the assignment. This

is rarely what you want

if (x = 3) ...

This does not test if x is 3. This sets x to the value 3, and then returns the 3 to the if for

testing. 3 is not 0, so it counts as "true" every time. This is probably the single most

common error made by beginning C programmers. The problem is that the compiler is no

help -- it thinks both forms are fine, so the only defense is extreme vigilance when

coding. Or write "= ≠ ==" in big letters on the back of your hand before coding. This

mistake is an absolute classic and it's a bear to debug. Watch Out! And need I say:

"Professional Programmer's Language."

Logical Operators

The value 0 is false, anything else is true. The operators evaluate left to right and stop as

soon as the truth or falsity of the expression can be deduced. (Such operators are called

"short circuiting") In ANSI C, these are furthermore guaranteed to use 1 to represent true,

and not just some random non-zero bit pattern. However, there are many C programs out

there which use values other than 1 for true (non-zero pointers for example), so when

programming, do not assume that a true boolean is necessarily 1 exactly.

! Boolean not (unary)

&& Boolean and

|| Boolean or

Bitwise Operators

C includes operators to manipulate memory at the bit level. This is useful for writing low-

level hardware or operating system code where the ordinary abstractions of numbers,

characters, pointers, etc... are insufficient -- an increasingly rare need. Bit manipulation

code tends to be less "portable". Code is "portable" if with no programmer intervention it

compiles and runs correctly on different types of computers. The bitwise operations are

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