c语言设计文法

C语言的文法可以用BNF（巴克斯-诺尔范式）表示，如下：

<program>    ::= <declaration-list>

<declaration-list> ::= <declaration>
                      | <declaration-list> <declaration>

<declaration> ::= <var-declaration>
                 | <fun-declaration>

<var-declaration> ::= <type-specifier> <id-list> ;

<type-specifier> ::= int
                    | float
                    | char

<id-list> ::= <id>
             | <id-list> , <id>

<id> ::= <identifier>
        | <identifier> = <expression>

<fun-declaration> ::= <type-specifier> <identifier> ( <params> ) <compound-stmt>

<params> ::= <param-list>
            | void

<param-list> ::= <param>
                | <param-list> , <param>

<param> ::= <type-specifier> <identifier>

<compound-stmt> ::= { <local-declarations> <statement-list> }

<local-declarations> ::= <var-declaration>
                        | <local-declarations> <var-declaration>

<statement-list> ::= <statement>
                     | <statement-list> <statement>

<statement> ::= <expression-stmt>
                | <compound-stmt>
                | <selection-stmt>
                | <iteration-stmt>
                | <return-stmt>

<expression-stmt> ::= <expression> ;
                     | ;

<selection-stmt> ::= if ( <expression> ) <statement>
                     | if ( <expression> ) <statement> else <statement>

<iteration-stmt> ::= while ( <expression> ) <statement>

<return-stmt> ::= return ;
                  | return <expression>

<expression> ::= <var> = <expression>
                 | <simple-expression>

<var> ::= <identifier>
         | <identifier> [ <expression> ]

<simple-expression> ::= <additive-expression> <relop> <additive-expression>
                        | <additive-expression>

<additive-expression> ::= <term>
                          | <additive-expression> + <term>
                          | <additive-expression> - <term>

<term> ::= <factor>
           | <term> * <factor>
           | <term> / <factor>

<factor> ::= ( <expression> )
             | <var>
             | <call>
             | <number>

<call> ::= <identifier> ( <args> )

<args> ::= <arg-list>
           | void

<arg-list> ::= <expression>
               | <arg-list> , <expression>

<relop> ::= <=
            | <
            | >=
            | >
            | ==
            | !=

其中，`<program>`是C语言程序的起始符号，整个程序由一个或多个声明组成；`<declaration>`可以是变量声明或函数声明；`<var-declaration>`定义变量的类型和标识符；`<fun-declaration>`定义函数的返回类型、函数名、参数类型和参数名；`<compound-stmt>`包含局部变量声明和语句列表；`<statement>`包括表达式语句、复合语句、选择语句、循环语句和返回语句；`<expression>`是算术或关系表达式；`<var>`表示变量或数组元素；`<call>`表示函数调用；`<args>`表示函数参数；`<relop>`表示关系运算符。