The C Programming Language 读书笔记（Chapter 1）

In this Chapter, a lot of examples are presented to introduce the basics used to write useful programs.
包括：Variables and Arithmetic, the for statement, Symbolic constants, Character input and output, Arrays,
Functions, Arguments, Character Arrays, External Variables.
这些知识很多知识复习而已。编了这么久的程序，这些知识还是掌握了。

这章包含了许多基本的概念，主要有：
functions, variables, statements, arguments, character string (= string constant)
loops, formatted output,  symbolic constants (使用#define以去掉programs中的magic Numbers）
text stream， character constants (between single qutote), Arrays, function prototype,
call by value, call by reference, external variables and scope, automatic variables.

文件处理的常见模式char by char为：
int c;
while ((c = getchar()) != EOF) {
 if (c 满足条件) {
  ... // 处理
 }
 ... // putchar(c);
}
文本处理常见模式word by word为：
int c, state;

state = OUT;
whiel ((c = getchar()) != EOF) {
 if (c == ' ' || c == '/n' || c == '/t')
  state = OUT;
 else if (state == OUT) {
  state = IN;
 }
 
 if (state == IN) {
  ... // c为当前word中的字符
 }
}

文本处理常见模式line by line为：
#define MAXLINE 1000 /* maximum input line length */

int getline(char line[], int maxline);

int len; /* current line length */
char line[MAXLINE]; /* current input line */

while ((len = getline(line, MAXLINE)) > 0) {
 ... // 处理line
}

/* getline: read a line into s, return length */
int getline(char s[], int lim)
{
 int c, i;

 for (i=0;i < lim-1 && (c=getchar())!=EOF && c!='/n';++i)
  s[i] = c;
 if (c == '/n') {
  s[i] = c;
  ++i;
 }
 s[i] = '/0';
 return i;
}
动词：
write (programs）
create, compile, load, run (programs)
on the Unix operating system
type (command)
print
call (functions)
define (function, variables)
declare (...)
in braces ({})
indent (statements)
read, write (characters, lines)
return (values)
execute
terminate