[educoder] 用YACC(BISON)生成语法分析和翻译器
第一关
/* 逆波兰符号计算器 */ /* 功能：能够计算出合法的后缀表达式的值，包括加法、减法、乘法、除法、乘方、取反等运算 */ /* 说明：在下面的begin和end之间添加代码，加油吧！ */ /* 提示： */%{ #include <ctype.h> #include <stdio.h> #include <math.h> int yylex (void); void yyerror (char const *);%}%define api.value.type {double}%token NUM%% /* Grammar rules and actions follow. */input: %empty| input line;line: 'n'| exp 'n' { printf ("%.10gn", $1); };exp: NUM { $$ = $1; } /* begin: add your code */ | exp exp '+' {$$ = $1 + $2;} | exp exp '-' {$$ = $1 - $2;} | exp exp '*' {$$ = $1 * $2;} | exp exp '/' {$$ = $1 / $2;} | exp exp '^' {$$ = pow($1, $2);} | exp 'n' {$$ = -$1;} /* end: add your code */;%%/* The lexical analyzer returns a double floating point number on the stack and the token NUM, or the numeric code of the character read if not a number. It skips all blanks and tabs, and returns 0 for end-of-input. */int yylex (void){ int c; /* Skip white space. */ while ((c = getchar ()) == ' ' || c == 't') continue; /* Process numbers. */ if (c == '.' || isdigit (c)) { ungetc (c, stdin); scanf ("%lf", &yylval); return NUM; } /* Return end-of-input. */ if (c == EOF) return 0; if (c == '!') return 0; /* Return a single char. */ return c;}int main (int argc, char** argv){ return yyparse();}/* Called by yyparse on error. */void yyerror (char const *s){ fprintf (stderr, "%sn", s);};第二关
/* 后缀转中缀 *//* 功能：后缀表达式转换成中缀表达式，包括加法、减法、乘法、除法等运算 *//* 说明：在下面的begin和end之间添加代码，加油吧！ */%{#include <stdio.h>#include <stdlib.h>#include <ctype.h>#include <string.h>#ifndef YYSTYPE#define YYSTYPE char*#endifchar idStr[50];char numStr[50];int yylex() ;extern int yyparse() ;FILE* yyin;void yyerror(const char* s);%}%token ADD%token MUL%token SUB%token DIV%token LB%token RB%token NUMBER%token ID%left ADD MUS%left MUL DIV%right UMINUS%%lines : lines expr {printf("%sn",$2);} | lines | ; /* begin: add your code*/ expr : expr expr ADD { $$ = (char *)malloc(200*sizeof(char)); strcpy($$,"("); strcat($$,$1); strcat($$,"+"); strcat($$,$2); strcat($$,")"); } | expr expr SUB { $$ = (char *)malloc(200*sizeof(char)); strcpy($$,"("); strcat($$,$1); strcat($$,"-"); strcat($$,$2); strcat($$,")"); } | expr expr MUL { $$ = (char *)malloc(200*sizeof(char)); strcpy($$,"("); strcat($$,$1); strcat($$,"*"); strcat($$,$2); strcat($$,")"); } | expr expr DIV { $$ = (char *)malloc(200*sizeof(char)); strcpy($$,"("); strcat($$,$1); strcat($$,"/"); strcat($$,$2); strcat($$,")"); } | SUB expr %prec UMINUS { strcpy($$,"-"); strcat($$,$2); } | NUMBER { $$ = (char *)malloc(200*sizeof(char)); strcpy($$,$1); } | ID { $$ = (char *)malloc(200*sizeof(char)); strcpy($$,$1); } ; /* end: add your code */;%%// programs sectionint yylex(){ char t;while(1){t = getchar();if(t==' ' || t =='t'|| t == 'n') {}else if(t == '+'){return ADD;}else if(t == '*'){return MUL;}else if(t == '-'){return SUB;}else if(t == '/'){return DIV;}else if(t>='0'&&t<='9'){int ti = 0; while (t>='0'&&t<='9'){ numStr[ti]=t; t = getchar(); ti++; } numStr[ti] = ' '; yylval = numStr; ungetc(t,stdin); return NUMBER;} else if(('a'<=t&&t<='z')||('A'<=t&&'Z'>=t)||(t=='_')){ int ti=0; while(('a'<=t&&t<='z')||('A'<=t&&'Z'>=t)||(t=='_')||(t>='0'&&t<='9')){ idStr[ti] = t; ti++; t=getchar(); } idStr[ti] = ' '; yylval = idStr; ungetc(t,stdin); return ID; } else{return t;}}}int main(void){ yyin = stdin; do { yyparse () ; } while (!feof(yyin)) ; return 0; }void yyerror(const char* s) { fprintf(stderr,"Parse error : %sn",s) ; exit(1);}