采用递归下降法实现while 循环语句的翻译设计

#define MAX 100 #include<iostream.h> #include<stdio.h> #include<string.h> char str[MAX]; char ch; int turn; char strToken[MAX]; int kind; int n=0;//存放strtoken[]元素的个数 struct Word//结构体 存放单词 { int sort; char word[MAX];//存放strtoken[]的内容 }; //record[x]=new Word; Word *record[12];//放所有识别出来的单词，分别存放他们的编号以及字符串，x是其下标 ////////////////////词法分析/////////////////////// int buffer()//载入 { int i=0; cout<<"输入程序，以“#”作为结束标志。"<<endl; for(int n=0;n<=MAX;n++) { for(;i<=MAX;i++) { scanf("%c",&str[i]); /////////////cin>>str[i]不可用，用C语言读入字符。 if(str[i]=='#') break;///////如果尾数为识别码#,则表示程序读完,跳出循环. } break; } return(i); } bool IsLetter(char ch)///////////判断是否是字母 { if(ch>=65&&ch<=90||ch>=97&&ch<=122) return(true); else return(false); } bool IsDigit(char ch)//////////判断是否是数字 { if(ch>=48&&ch<=57) return(true); else return(false); } char GetChar(int i)///////读取字符 { char ch; ch=str[i]; return(ch); } char GetBC(char ch)////判断是不是空格或者换行，如果是，直接读取下一个字符直道不再空白为止 { if(ch==32||ch==10) { turn++; ch=GetChar(turn); ch=GetBC(ch);/////////递归实现 return(ch); } else return(ch); } void Concat()/////////////连接，即为strtoken[]赋值 { strToken[n]=ch; n++; } int Reserve()/////以单词为单位查找保留字，是则返回编码，不是则返回0，用来区分标志符和保留字 { if(strcmp(strToken," DIM\0")==0)///////调用strcmp函数实现, return(1); else if(strcmp(strToken,"for\0")==0) return(2); else if(strcmp(strToken,"step\0")==0) return(3); else if(strcmp(strToken,"until\0")==0) return(4); else if(strcmp(strToken,"do\0")==0) return(5); else return(6); } void clear() { n=0; } /////////////*语法递归分析*///////////////// int A(int * c,int & q) { if(c[q++]==3) { if(c[q]==7) { q++; return 1; } else {cout<<"step右部出错"<<endl;return 0;} }else {cout<<"error 'step'"<<endl;return 0;} } int B(int * b,int & o) { if(b[o++]==4) { if(b[o]==7) { o++; return 1; } else {cout<<"until右部出错"<<endl;return 0;} }else {cout<<"error 'until'"<<endl;return 0;} } int S2(int * d,int & h) { if(d[h++]==6) { if(d[h++]==8) { if((d[h]==6||d[h]==7)) {h++; return 1;} else {cout<<"赋值语句右部出错 "<<endl;return 0;} }else {cout<<"赋值语句缺少赋值运算符 "<<endl;return 0;} }else {cout<<"赋值语句左部出错 "<<endl;return 0;} } int S1(int * m,int & n) { if(S2(m,n)) { if(A(m,n)) { if(B(m,n)) return 1; else return 0; }else return 0; }else return 0; } int S(int *a,int & z) { if (a[z++]==2) { if (S1(a,z)) { if(a[z++]==5) { if(S2(a,z)) { cout<<"succeed!"<<endl;return 1; }else return 0; }else {cout<<"error 'do'"<<endl; return 0;} }else return 0; }else {cout<<"error 'for'"<<endl; return 0;} } void main() { cout<<"*************产生式***************"<<endl;// for step until do i j = cout<<" S ->for S1 do S2"<<endl; // 编号 2 3 4 5 6 7 8 cout<<" S1 ->S2AB"<<endl; cout<<" S2 ->i=j"<<endl; cout<<" A ->stepj"<<endl; cout<<" B ->untilj"<<endl; int num; turn=0; num=buffer()-1; int x=0;//计识别的单词的个数 for(;turn<=num;turn++)//总循环,ch存放刚读入的字符，strtoken[]存放已识别的标志付或保留字，turn是数组str[]的下标 { ch=GetChar(turn); ch=GetBC(ch); if(IsLetter(ch)) { while(IsLetter(ch)&&turn<=num||IsDigit(ch)&&turn<=num) { Concat(); ch=GetChar(++turn); } strToken[n]='\0'; ch=NULL;//此ch不是标志符中的符号 turn=turn-1; kind=Reserve(); record[x]=new Word; record[x]->sort=kind;//12345或6 //cout<<kind; //测试 cout<<"("; for(int i=0;i<n;i++) { record[x]->word[i]=strToken[i]; cout<<record[x]->word[i];//输出识别的标志符或保留字 } cout<<","<<kind<<")"<<endl; record[x]->word[i]='\0'; clear(); x++; } else if(IsDigit(ch)) { while(IsDigit(ch)&&turn<=num) { Concat(); ch=GetChar(++turn); } ch=NULL; turn=turn-1; kind=7; ////////////// record[x]=new Word; record[x]->sort=kind; //////////////// cout<<"("; for(int i=0;i<n;i++) { record[x]->word[i]=strToken[i]; cout<<record[x]->word[i]; } cout<<","<<kind<<")"<<endl; record[x]->word[i]='\0'; clear();x++; } else if(ch=='=') { kind=8; /////// record[x]=new Word; record[x]->word[0]='='; record[x++]->sort=kind; cout<<"(=,"<<kind<<")"<<endl; } else cout<<"error input!"<<endl; } //////////////////////*语法分析*//////////////// //int y; /*for(y=0;y<x;y++) {cout<<record[y]->sort<<" ";//打印单词的编号 。 }cout<<endl;*/ int ana[MAX];//存放词法分析得到的单词序列的编号的序列 int m; for(m=0;m<x;m++) { ana[m]=record[m]->sort;//将sort作为数组保存起来 } /////////语法分析/////// int j=0; ///////////////////制导翻译////////////////// if(!S(ana,j)) cout<<"语法出错!"<<endl; else { cout<<"三地址码如下："<<endl; cout<<"100 "; int i=0; while(record[1]->word[i]!='\0') cout<<record[1]->word[i++];cout<<record[2]->word[0]; i=0; while(record[3]->word[i]!='\0') cout<<record[3]->word[i++];cout<<endl; cout<<"101 goto 103"<<endl; cout<<"102 "; i=0; while(record[1]->word[i]!='\0') cout<<record[1]->word[i++];cout<<":="; i=0; while(record[1]->word[i]!='\0') cout<<record[1]->word[i++];cout<<"+"; i=0; while(record[5]->word[i]!='\0') cout<<record[5]->word[i++];cout<<endl; cout<<"103 if "; i=0; while(record[1]->word[i]!='\0') cout<<record[1]->word[i++];cout<<"<"; i=0; while(record[7]->word[i]!='\0') cout<<record[7]->word[i++]; cout<<" goto 105"<<endl; cout<<"104 goto 107"<<endl; cout<<"105 "; i=0; while(record[9]->word[i]!='\0') cout<<record[9]->word[i++];cout<<":="; i=0; while(record[11]->word[i]!='\0') cout<<record[11]->word[i++];cout<<endl; cout<<"106 goto 102"<<endl; cout<<"107 end"<<endl; } }