编译原理课后作业【自顶向下分析法】语法分析

实验二：

题目：语法分析

目的：通过该实验掌握描述语法的文法和自顶向下分析法中的预测分析法。

要求：对给定的文法建立预测分析表；利用预测分析法对实验一的结果进行语法分析，对不符合给定文法的表达式给出出错位置信息。

内容：给定描述语法的文法为：

E->E+T|T

T->T*F|F

F->i|(E)

题目如上描述。

用了STL里的MAP写了个程序，写的比较简单也可能有BUG，欢迎大家指出修正

Source code:

  1 //Jeremy Wu {Wushuaiyi} CS1301
  2 //#pragma comment(linker, "/STACK:16777216") //for c++ Compiler
  3 #include <stdio.h>
  4 #include <iostream>
  5 #include <climits>
  6 #include <cstring>
  7 #include <stack>
  8 #include <vector>
  9 #include <map>
 10 #include <algorithm>
 11 #define ll long long
 12 using namespace std;
 13
 14 const int INF = 0x3f3f3f3f;
 15 const int MAXN = 8;
 16 const int LEN = 10000;
 17 int iCount;
 18 string ee = "e";                //Epsilon express
 19 string hh;                      //Handle
 20 string now, cur;                //Solve Handle
 21 vector <string> a, b;           //Stack and input array
 22 map <string, int> Map;          //Map
 23 map <int, string> Map_out;      //Map_out
 24 int Real[MAXN][MAXN];           //Map_realation
 25 void init(){
 26     iCount = 1;
 27     a.clear();
 28     b.clear();
 29     Map.clear();
 30     Map_out.clear();
 31     memset(Real, 0, sizeof(Real));
 32     Map["E"] = 1, Map["E‘"] = 2, Map["T"] = 3, Map["T‘"] = 4, Map["F"] = 5;
 33     Map["i"] = 6, Map["+"] = 7, Map["*"] = 8, Map["("] = 9, Map["#"] = 10;
 34     Map_out[11] = "TE‘", Map_out[12] = "+TE‘", Map_out[13] = "e";
 35     Map_out[14] = "FT‘", Map_out[15] = "*FT‘", Map_out[16] = "(E)", Map_out[17] = "i";
 36     Real[Map["E"]][Map["i"]] = 11, Real[Map["E"]][Map["("]] = 11,
 37     Real[Map["E‘"]][Map["+"]] = 12, Real[Map["E‘"]][Map[")"]] = 13,
 38     Real[Map["E‘"]][Map["#"]] = 13, Real[Map["T"]][Map["i"]] = 14,
 39     Real[Map["T"]][Map["("]] = 14, Real[Map["T‘"]][Map["+"]] = 13,
 40     Real[Map["T‘"]][Map["*"]] = 15, Real[Map["T‘"]][Map[")"]] = 13,
 41     Real[Map["T‘"]][Map["#"]] = 13, Real[Map["F"]][Map["i"]] = 17,
 42     Real[Map["F"]][Map["("]] = 16;
 43 }
 44
 45 void LookAhead(){
 46     for(int i = hh.size() - 1; i >= 0; --i){
 47         string tt;
 48            if(hh[i] == ‘\‘‘ && hh[i - 1] == ‘E‘){
 49                b.push_back("E‘");
 50             --i;
 51         } else if(hh[i] == ‘\‘‘ && hh[i - 1] == ‘T‘){
 52                b.push_back("T‘");
 53             --i;
 54         } else{
 55                tt = hh[i];
 56             b.push_back(tt);
 57         }
 58     }
 59 }
 60
 61 void print(){
 62     cout << "iCount = " << iCount << endl;
 63     cout << "Stack : " ;
 64     for(int i = 0; i < b.size(); ++i){
 65         cout << b[i];
 66     }
 67     cout << endl << "Input : ";
 68     for(int i = a.size()- 1; i >= 0; --i){
 69         cout << a[i];
 70     }
 71     cout << endl << endl;
 72 }
 73
 74 bool ErrorReport(){
 75     map<int, string>::iterator iter;
 76     iter = Map_out.find(Real[Map[now]][Map[cur]]);
 77     if(iter == Map_out.end()){
 78         cout << "Error" << endl;
 79         return true;
 80     }
 81     return false;
 82 }
 83
 84 int main(){
 85     int i;
 86     char ch[LEN];
 87     init();
 88     cin >> ch;
 89         a.push_back("#");
 90     for(i = strlen(ch); i >= 0; --i){
 91         string temp;
 92         temp = ch[i];
 93         a.push_back(temp);
 94     }
 95     b.push_back("#");
 96     b.push_back("E");
 97     print();
 98     while(!a.empty()){
 99         ++iCount;
100         cur = a.back();
101         now = b.back();
102         b.pop_back();
103         if(cur == now){                                     //Reduce
104             a.pop_back();
105         } else{                                             //Shift
106             if(ErrorReport()){
107                 return 0;                                    //Exit Program
108             }
109             hh = Map_out[Real[Map[now]][Map[cur]]];
110             if(hh == ee){
111                 print();
112                 if(b.back() == "#"){
113                     cout << "Accecpt" << endl;              //Exit Program
114                     return 0;
115                 }
116                 continue;
117             }
118             LookAhead();
119         }
120         print();
121     }
122     return 0;
123 }