C-

C MINUS是C语言的一个子集，该语言的语法在《编译原理与实践》第九章附录中有详细的介绍。

Lexical Conventions

  1. 关键字
    else if int return void while
  2. 专用符号
    + - * / < <= > >= == != = ; , ( ) [ ] { } /* */

  3. 标识符ID和整数NUM，通过下列正则表达式定义:
    ID=letter letter*
    NUM=digit digit*
    letter = a|...|z|A|...|Z
    digit = 0|...|9

  4. 注释用/*...*/表示，可以超过一行。注释不能嵌套。
    /*...*/

思考

  1. 识别C-语言Token的DFA设计
  2. note that: [, ], 和 [] 是三种不同的tokens。[]用于声明数组类型，[]中间不得有空格。

Syntax

  1. program → declaration-list
  2. declaration-list → declaration-list declaration declaration
  3. declaration → var-declaration fun-declaration
  4. var-declaration → type-specifier ID ; type-specifier ID [ NUM ];
  5. type-specifier → int void
  6. fun-declaration → type-specifier ID (params) compound-stmt
  7. params → param-list void
  8. param-list→ param-list , param param
  9. param → type-specifier ID type-specifier ID []
  10. compound-stmt → { local-declarations statement-list }
  11. local-declarations → local-declarations var-declaration empty
  12. statement-list → statement-list statement empty
  13. statement → expression-stmt compound-stmt selection-stmt
      iteration-stmt return-stmt
  14. expression-stmt → expression ; ;
  15. selection-stmt → if ( expression ) statement if ( expression ) statement else statement
  16. iteration-stmt → while ( expression ) statement
  17. return-stmt → return ; return expression ;
  18. expression → var = expression simple-expression
  19. var → ID ID [ expression ]
  20. simple-expression → additive-expression relop additive- expression additive-expression
  21. relop → <= < > >= == !=
  22. additive-expression → additive-expression addop term term
  23. addop → + -
  24. term → term mulop factor factor
  25. mulop → * /
  26. factor → ( expression ) var call NUM
  27. call → ID ( args )
  28. args → arg-list empty
  29. arg-list → arg-list , expression expression

思考：

  1. C-语言语法的特点，它的CFG

Sample Programs of C-

int gcd (int u, int v) { /* calculate the gcd of u and v */
    if (v == 0) return u;
    else return gcd(v, u - u / v * v); /* v,u-u/v*v is equals to u mod v*/
}
int main() {
    int x; int y; int temp;
    x = 72;
    y = 18;
    if (x<y) {
        temp = x;
        x = y;
        y = temp;
    }
    gcd(x,y);
    return 0;
}