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Create a recursive descent parser for a C grammar subset using C++ assignment help

The assignment deals with implementing a program in C++ to parse a subset of the C grammar. Our C++ assignment helpers have developed a program that implements both a lexical analyzer and a parser to analyze the source files. The program allows the user to enter the file name of the source to be parsed and it calls the corresponding functions to scan and parse the code. The result of the parsing is printed on the screen. If an error is found, the corresponding line and error are printed on the screen.

Scanning and Parsing C Code

#pragma once #include #include #include #include #include #include #include using namespace std; #define N_RESERVED_WORDS 9 enum { ift, elset, whilet, floatt, integert, chart, breakt, continuet, voidt, addopt, mulopt, assignopt, relopt, lparent, rparent, lbracet, rbracet, lbrkt, rbrkt, commat, semit, periodt, valuet, valuert, idt, stringt, eoft, unknownt }; const char *TYPE[] = { "ift", "elset", "whilet", "floatt", "integert", "chart", "breakt", "continuet", "voidt", "addopt", "mulopt", "assignopt", "relopt", "lparent", "rparent", "lbracet", "rbracet", "lbrkt", "rbrkt", "commat", "semit", "periodt", "valuet", "valuert", "idt", "stringt", "eoft", "unknownt" }; const char *PRINT[] = { "if", "else", "while", "float", "int", "char", "break", "continue", "void", "+, - or ||", "*, /, %% or &&", "=", "==, !=, <, <=, > or >=", "(", ")", "{", "}", "[", "]", ",", ";", ".", "valuet", "valuert", "idt", "stringt", "eoft", "unknownt" }; const char *RESERVED_WORDS[] = {"if","else","while","float","int","char","break","continue","void"}; int RVALS[] = {ift,elset,whilet,floatt,integert,chart,breakt,continuet,voidt}; // class used to perform the lexical analysis class LexicalAnalyzer { private: string code; // variable to hold the code to analyze int pos; // current character position in code public: int nline; // current line number in code int Token; string Lexeme; int Value; float ValueR; string Literal; LexicalAnalyzer(string filename) { code=loadFile(filename); pos=0; nline=1; } // function that returns true if the given character is a letter bool isLetter(char c) { if(c>='a' && c<='z') return true; if(c>='A' && c<='Z') return true; return false; } // function that returns true if the given character is a digit bool isDigit(char c) { if(c>='0' && c<='9') return true; return false; } // get the next token in the code file void GetNextToken() { int start; int state=0; int type; while(state>=0 && pos<=code.length()) { char ch=code[pos++]; switch(state) { case 0: // initial state start=pos-1; if(isLetter(ch)) state=1; else if(isDigit(ch)) state=2; else { switch(ch) { case '/': state=5; break; case '=': state=8; break; case '!': state=9; break; case '<': state=9; break; case '>': state=9; break; case '+': case '-': state=10; break; case '|': state=11; break; case '*': state=12; break; case '%': state=12; break; case '&': state=13; break; case '(': type=lparent; state=14; break; case ')': type=rparent; state=14; break; case '{': type=lbracet; state=14; break; case '}': type=rbracet; state=14; break; case '[': type=lbrkt; state=14; break; case ']': type=rbrkt; state=14; break; case ',': type=commat; state=14; break; case ';': type=semit; state=14; break; case '.': type=periodt; state=14; break; case '"': state=15; break; case '\n': nline++; break; case ' ': case '\t': break; case 0: state=-100; break; // end of file default: cout << "Error: invalid character "<< ch <<" in line " << nline << endl; exit(1); } } break; case 1: //idt if(!isLetter(ch) && !isDigit(ch) && ch!='_') { state=-1; // end reading token pos--; // try same char again } break; case 2: //digits if(!isDigit(ch)) { if(ch!='.') { state=-2; pos--; // try same char again } else state=3; } break; case 3: //numt if(!isDigit(ch)) { cout << "Error: unexpected character after . in line" << nline << endl; exit(1); } else state=4; break; case 4: // real if(!isDigit(ch)) { state=-3; pos--; // try same char again } break; case 5: if(ch=='*') state=6; else { state=12; // mulop / pos--; // try same char again } break; case 6: // comment if(ch=='*') // first char of ending comment state=7; break; case 7: if(ch=='/') // end of comment state=0; else state=6; break; case 8: if(ch=='=') state=-4; // relop == else { type=assignopt; state=-5; // assignop = pos--; // try same char again } break; case 9: // relop if(ch=='=') state=-4; else { if(code[pos-2]=='!') { cout << "Error: invalid character ! in line " << nline << endl; exit(1); } state=-4; pos--; } break; case 10: // addop pos--; // try same char again state=-6; break; case 11: if(ch=='|') state=-6; //addop || else { cout << "Error: invalid character | in line " << nline << endl; exit(1); } break; case 12: // mulop pos--; // try same char again state=-7; break; case 13: if(ch=='&') state=-7; //mulop && else { cout << "Error: invalid character & in line " << nline << endl; exit(1); } break; case 14: // other symbols pos--; // try same char again state=-8; //symbol break; case 15: //string literal if(ch=='"') state=-9; else if(ch=='\n') { cout << "Error: missing closing \" for string in line " << nline << endl; exit(1); } break; } } if(state>0) { cout << "Error: unexpected end of file found in line " << nline << endl; exit(1); } else { Lexeme=code.substr(start,pos-start); switch(state) { case -1: // idt Token=idt; for(int i=0; i27) { cout << "Error: identifier " << Lexeme << " in line " << nline << " is too long."<< endl; exit(1); } break; case -2: // integer Token=valuet; Value=atoi(Lexeme.c_str()); break; case -3: // real Token=valuert; ValueR=atof(Lexeme.c_str()); break; case -4: // relop Token=relopt; break; case -5: // assignop Token=assignopt; break; case -6: //addop Token=addopt; break; case -7: //mulop Token=mulopt; break; case -8: //symbol Token=type; break; case -9: //string Token=stringt; Literal=Lexeme; break; case -100: // eof Token=eoft; } } } // read all the file and return it as a string string loadFile(string filename) { ifstream input(filename.c_str()); if(!input.is_open()) { cout << "Error opening file: " << filename << endl; exit(1); } stringstream ss; ss << input.rdbuf(); return ss.str(); } string printCurrentToken() { stringstream ss; switch(Token) { case valuet: ss << Value; break; case valuert: ss << ValueR; break; case stringt: ss << "\"" << Literal << "\""; break; case eoft: ss << "EOF" ; break; case idt: ss << Lexeme; break; default: ss << PRINT[Token]; } return ss.str(); } string printToken(int symbol) { stringstream ss; switch(symbol) { case valuet: ss << "Integer Value"; break; case valuert: ss << "Real Value"; break; case stringt: ss << "Literal"; break; case eoft: ss << "EOF" ; break; case idt: ss << "Identifier"; break; default: ss << PRINT[symbol]; } return ss.str(); } }; #include "LexicalAnalyzer.h" #include "Parser.h" // main program int main() { string filename; cout << "Please enter the name of the file to load: "; getline(cin,filename); LexicalAnalyzer lex(filename); // create lexical analyzer Parser parser(lex); // create parser parser.parse(); // do the parsing return 0; } #include #include // Recursive parser class class Parser { private: LexicalAnalyzer lex; // if the current symbol is equal to the symbol needed, return true // and advance to next symbol else return false bool accept(int symbol) { if(lex.Token==symbol) { lex.GetNextToken(); return true; } else return false; } // if the current symbol is equal to the expected symbol argument, return true // and advance to next symbol else generates an error void expect(int symbol) { if(!accept(symbol)) { cout << "Error: unexpected symbol: " << lex.printCurrentToken() << " in line " << lex.nline << ", expected "<< lex.printToken(symbol) << endl; exit(1); } } // parse for the TYPE part from the grammar bool parseType() { if(lex.Token==floatt || lex.Token==integert || lex.Token==chart) { lex.GetNextToken(); return true; } else return false; } // parse for the PARAMTAIL part from the grammar void parseParamTail() { if(accept(commat)) { if(parseType()) { expect(idt); parseParamTail(); } else { cout << "Error: unexpected symbol: " << lex.printCurrentToken() << " in line " << lex.nline << ", unknown type" << endl; exit(1); } } } // parse for the PARAMLIST part from the grammar void parseParamList() { if(parseType()) { expect(idt); parseParamTail(); } } // parse for the STAT_LIST part from the grammar void parseStatList() { //empty } // parse for the RET_STAT part from the grammar void parseRetStat() { //empty } // parse for the IDTAIL part from the grammar void parseIdTail() { if(accept(commat)) { expect(idt); parseIdTail(); } } // parse for the IDLIST part from the grammar void parseIdList() { expect(idt); parseIdTail(); expect(semit); parseDecl(); } // parse for the DECL part from the grammar void parseDecl() { if(parseType()) parseIdList(); } // parse for the COMPOUND part from the grammar void parseCompound() { expect(lbracet); parseDecl(); parseStatList(); parseRetStat(); expect(rbracet); } // parse for the REST part from the grammar void parseRest() { if(accept(lparent)) { parseParamList(); expect(rparent); parseCompound(); } else { parseIdTail(); expect(semit); parseProgram(); } } // parse for the PROG part from the grammar void parseProgram() { if(parseType()) { expect(idt); parseRest(); parseProgram(); } } public: // constructor for the class saves the lexical analyzer for using it in the parsing Parser(LexicalAnalyzer Lexa) : lex(Lexa) { } // parse is the main function used to start parsing the program in the lexer void parse() { lex.GetNextToken(); parseProgram(); if(lex.Token==eoft) cout << "Program parsing ended successfully." << endl; else cout << "Error: unexpected symbol: " << lex.printCurrentToken() << " in line " << lex.nline << ", expected end of file" << endl; } };