Lexical Elements, Operators, and the C System

1
Chapter 2

• 3? ??
• Lexical Elements, Operators, and the C System

2
Compiler

• Grammar lexical, syntax,
• semantics, pragmatics
• Compiler checks the legality of C code
• Preprocessor ? compiler
• Error recovery

3
Lexical Terms

• Token? ?? (ANSI C)
• keywords, identifiers, constants, string
  constants, operators, punctuators
• Lexical errors

4
Characters and Lexical Elements

• Lowercase letters, uppercase letters, digits,
  other characters (, -, ), white space
  characters (blank, newline, tab)
• Lexical errors
• int a, b, c ? inta, b, c
• a, b a , b
• sumab sum a b ? s u m a b

5
Syntax Rules

• Digit 0123 456789
• BNF(Bacus Naur Form)
• (rewriting), (separate),
• (optional), (0 or more),
• 1, 0, 1, opt
• conditional_statement if (expression)
• statement
• else statementopt

6
??(identifier)

• identifier
• letter _1 letter digit _0
• ?? constant(??, ??), string? ?? ??(BNF)? ???
  2.74, 36, 2.7e-04, I love you.? ??? ???.
  (constant? string?)
• Appendix B? ???? ?? !!!!

7
Comments

• / This is comments /
• // This is comments
• Self-documentation
• ??? ?? documentation? ??? ???

8
Keywords

• Auto, do, goto, signed (page 77)
• Reserved word? ??? ?? word? ???
• Keyword? reserved? ??? ??? ?? ??

9
Constants, String constants,Operators, Punctuator

• Constants 0, 17, 3,14159, a, , \n,
  enumeration type
• String constants I, a string, ,
  cab, \\ I \\
• abc def ? abcdef
• ??? / This is a string /,
• Operators , -, , /, ??? a-b, a_b
• Punctuators , ,, , (, )
• ??? main(void)
• a, ab
• ?? ? ??? ??? ???

10
Precedence and Associativity of Operators

• Page 332? ?? ???

Operator precedence and associativity Operator precedence and associativity
Operator Associativity
() (postfix) --(postfix) left to right
(unary), -(unary), (prefix), --(prefix) right to left
/ left to right
- left to right
- / right to left
11
Increment and decrement Operators

• val, val valval1
• ???? ??? ???
• ??
• (1) a1 ba printf(d,d,a,b)
• (2) a1 ba printf(d,d,a,b)
• Side-effect

12
Assignment Operators

• abc / ? ????? ?? ????? ???? ??? ?? /
• variableright_side
• a (b2) (c3)
• ? b2 c3 abc / ?? ?? /
• abc0
• kk2 ? k2
• , , -, , /, , gtgt, ltlt, , ,
• / ?? gt, lt? ?? /
• i jk ? i (jk) ? iijk ? i(i(jk))

13
The C System(1)

• The preprocessor
• include ltstdio.hgt
• include ltstdio.hgt / int rand(void)? ?? /

14
The C System(2)

• random? ??? ????
• seed number ? srand(time(NULL))

15
?? ??? ? ??

• 2? 5,7,8,9? ??? ??? ?????? ????
• 10? ????.
• 20?? ????.
• 29? ????
• / ?? ???? ????? ??
• ?, ??? ??? ???? ??
• ?? ?? ??? ??? ??? /

16
??? ? ??

• 10, 15,17,18, 23, 25
• 27 (? ??? ?? ?? ????
• ??? ??)