designed_BNF.txt

Finally designed BNF

1. lexical level

1.1 operators & primitive character

<addsub_tk>  ::=    + | -
<multdiv_tk> ::=    * | /
<rltop_tk>   ::=    < | <= | > | >= | != | ==

<non-zero digit>    ::=     1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
<digit>             ::=     0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
<letter>            ::=     _ | a | ... | z | A | ... | Z

1.2 comlicate types

<chrlit_tk> ::= '<addsub_tk>' | '<multdiv_tk>' | '<letter>' | '<digit>'
<strlit_tk> ::= "{<support character, aka. a character whose ASCII code is 32, 33 or 35-126, according to the assignment requirement>}"
<intlit_tk> ::= <non-zero digit> {<digit>}
<id_tk>     ::= <letter> {<letter> | <digit>}



2. syntax level

2.1 simple elements

<nvtype>   ::= char | int
<integer>  ::= {+ | -} <intlit_tk> | 0


2.2 statements

<program>  ::= {<constdef> | void <funcdeftail> | <declheader> <funcdeftail> | <declheader> <vardeftail>)}

<constdef> ::= const <nvtype> <id>=<constant> {,<id>=<constant>} ;
<constant> ::= <integer> | <charlit>

<declheader>  ::= <nvtype> id
<vardeftail>  ::= ; | ‘[’ <intlit_tk> ‘]’ {, id | , id ‘[’ <intlit_tk> ‘]’} ;
<funcdeftail> ::= id ‘(’ [<paralist>]  ‘)’ ‘{’ <cmpdstmts> ‘}’
<paralist>    ::= <nvtype> <id> {,<nvtype> <id>}

<cmpdstmts>      ::= [<constdef>] [<declheader> <vardeftail>] <statement list>
<statement list> ::= {<statement>}
<statement>      ::= <if_stmt> | <while_stmt> | <switch_stmt>
                     | <funccall>;  | <assign_stmt>; | <scanf_stmt>;
                     | <printf_stmt>; | <return_stmt>; |  ‘{’<statement list>‘}’ | ;

<condition> ::= <expression> <rltop_tk> <expression> | <expression>
<if_stmt> ::= if ‘(’ <condition> ‘)’ <statement>
<while_stmt> ::= while ‘(’ <condition> ‘)’ <statement>
<switch_stmt> ::= switch ‘(’<expression>‘)’ ‘{’<switch list> [default: <statement>] ‘}’
<switch list> ::= case<constant>：<statement> { case<constant>：<statement> }

<return_stmt> ::= return <expression> ; | return;


<arglist>     ::= <expression> {,<expression>} | <empty>
<funccall>    ::= <id> ‘(’ <arglist> ‘)’
<printf_stmt> ::= printf ‘(’ <arglist> ‘)’
<scanf_stmt>  ::= scanf  ‘(’ <arglist> ‘)’
<assign_stmt> ::= <id> = <expression> | <id> ‘[’ <expression> ‘]’ = <expression>

2.3 expressions

<expression>    ::= <addsub_tk> <term> { <addsub_tk> <term> }
<term>          ::= <factor> { <multdiv_tk> <factor> }
<factor>        ::= <id> | <id> ‘[’ <expression> ‘]’ | ‘(’ <expression> ‘)’
                     | <integer> | <chrlit_tk> | <funccall>