c109f04t2 - CSE 109 Test 1 Monday 17 November 2004...

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CSE 109 Test 1 Monday 17 November 2004 >>>>>>>>>>>>>>>>>>>>>>SUGGESTED ANSWERS<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< 1. Assume the lexical analyzer from assignments p5-p8. Assume a language whose programs consist of zero or more lines of code, followed by a line with "END", where each line has one of the forms: READ <identifier> WRITE <identifier> <identifier>++ <identifier>-- Write a program that parses (determines syntactical correctness of) programs entered at the console (keyboard). The program should simply respond by stating whether the program is correct. Hint: Identifiers cannot be declared, so only one pass is needed. ========================================================================= class Parser {public: Parser():lex(){} void parse(); private: Lex lex; static void check(bool b, char * mess); }; } void main() {Parser p; p.parse(); } void Parser::parse() {int tok,savetok; tok=lex.next(); while(tok!=Lex::END) {switch(tok) {case Lex::WRITE: case Lex::READ: tok=lex.next(); check(tok==Lex::IDENT,"Identifier expected"); break; case Lex::IDENT: savetok=lex.next(); check(savetok==Lex::SPLUS || savetok==Lex::SMINUS, " '+' or '-' expected"); tok=lex.next(); check(tok==savetok," '++' or '--' expected"); break;
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