武汉大学编译原理第一次作业

/** 计科3 halfopen*第一次作业，老师不要求做思考题*问题二：XL语言分析器的结合次序和优先级, 用retsuff.exe对输入表达式: "1 + 2 + 3;",    先进行 1 + 2 的运算, 还是先进行 2 + 3 的运算.    输入"1+2*3;"，先算"2*3"，还是先算"1+2".答：Please input an infix expression and ending with ";"1+2*3;    t0 = 1    t1 = 2    t2 = 3    t1 *= t2    t0 += t1the affix expression is + 1 * 2 3输出结果如上，所以是先算2*3**//* retinf.c   AXL分析器 */#include <stdio.h>#include <string.h>#include <stdlib.h>#include "lex.h"char err_id[] = "error";char * midexp;extern char * yytext;struct YYLVAL {  char * val;  /* 记录表达式中间临时变量 */  char * expr; /* 记录表达式后缀式 */  int last_op;  /* last operation of expression    for elimination of redundant parentheses */};typedef struct YYLVAL Yylval;Yylval    *factor     ( void );Yylval    *term       ( void );Yylval    *expression ( void );char *newname( void ); /* 在name.c中定义 */char *getVar(void);extern void freename( char *name );void statements ( void ){  /*  statements -> expression SEMI  |  expression SEMI statements  */    Yylval *temp;  printf("Please input an affix expression and ending with \";\"\n");  while( !match(EOI) ){    temp = expression();    printf("the infix expression is %s\n", temp -> expr);    freename(temp -> val);    free(temp -> expr);    free(temp);        if( match( SEMI ) ){      advance();      printf("Please input an affix expression and ending with \";\"\n");    }    else      fprintf( stderr, "%d: Inserting missing semicolon\n", yylineno );  }}/**test */void print_var(Yylval *t){char op = yytext[0];printf("expr:%s val:%s last_op:%c\n",t->expr,t->val, op);}Yylval *expression(void){   /*    expression -> PLUS expression expression               |  MINUS expression expression               |  TIMES expression expression               |  DIVISION expression expression       |  NUM_OR_ID  */Yylval* temp;temp=(Yylval *) malloc(sizeof(Yylval));if(match(PLUS)||match(MINUS) || match(TIMES)|| match(DIVISION) ){ //for the first 4 cases;temp = term(); }else if(match(NUM_OR_ID)){ //for the last case;    temp = factor();}elseadvance();return temp;}Yylval *term(void){Yylval* temp;temp=(Yylval *) malloc(sizeof(Yylval));int type=0;if(match(TIMES)||match(DIVISION)) type = 1;char op=yytext[0];    advance();    Yylval* temp1=expression();    Yylval* temp2=expression();    printf("%s %c = %s\n",temp1->val,op,temp2->val);freename(temp2->val); //release unused register    temp->val=temp1->val;//update the register's numberif(type ==0){ temp->last_op=1;      temp->expr=(char *)malloc(strlen(temp1->expr)+1+strlen(temp2->expr));     sprintf( temp->expr, "%s %c %s",temp1->expr, op, temp2->expr);}else{temp->last_op=2;    if(temp1->last_op==1||temp2->last_op==1){     if(temp1->last_op!=1){ // a*(b+c)    temp->expr=(char *)malloc(strlen(temp1->expr)+3+strlen(temp2->expr));    sprintf(temp->expr,"%s %c %c %s %c",temp1->expr,op,'(',temp2->expr,')');}else if(temp2->last_op!=1){ // (a+c)*b    temp->expr=(char *)malloc(strlen(temp1->expr)+3+strlen(temp2->expr));    sprintf(temp->expr,"%c %s %c %c %s",'(',temp1->expr,')',op,temp2->expr); }else{//(a+b)*(c+d)    temp->expr=(char *)malloc(strlen(temp1->expr)+5+strlen(temp2->expr));    sprintf(temp->expr,"%c %s %c %c %c %s %c",'(',temp1->expr,')',op,'(',temp2->expr,')');    }}else{ //a+b+c    temp->expr=(char *)malloc(strlen(temp1->expr)+1+strlen(temp2->expr));    sprintf(temp->expr, "%s %c %s", temp1->expr, op, temp2->expr);  }}return temp;     }Yylval* factor(void){char *name;char *name1 = newname(); Yylval* temp;temp=(Yylval *) malloc(sizeof(Yylval));name = (char *) malloc(yyleng + 1);strncpy(name, yytext, yyleng);printf("%s = %s\n",name1,name);temp->expr=(char *)malloc(strlen(name));sprintf(temp->expr,"%s",name);temp->last_op=2;temp->val=name1;advance();return temp;}