// A simple parser for C/C++-style variable declarations. // THe grammar is as follows: // //  ::=   ; |   =  ; //  ::= int | float //  ::= A | B | C | D | E //  ::=  |  //  ::=   |  //  ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 //  ::=  .  // // Input is entered at the keyboard. // If the input is correct, the program should print // "no error found", otherwise, it should print the type // of error and terminate its execution. There are four // possible errors: // // "unrecognizable type" // "illegal variable name" // "unexpected number" // "; expected" // // Error message is printed out by calling function // "error". An error code ranging from 0 to 4 can be // passed as an argument to the function indicating what // message is to be printed. The mapping from the error // code to the message can be found by looking at the // definition of function "error". // // The following are some sample input and the response // from the program: // // Please enter a declaration in format   [= number] ; // int A; // no error found // // Please enter a declaration in format   [= number] ; // int a; // illegal variable name // // Please enter a declaration in format   [= number] ; // short B; // unrecognizable type // // Please enter a declaration in format   [= number] ; // float C = 0.5; // no error found // // Please enter a declaration in format   [= number] ; // int A = 10, // unexpected token #include  #include  using namespace std; string GetToken(); void error(int); int main() { string token; cout << "Please enter a declaration in format " << "  [= number] ;" << endl; token = GetToken(); // Write the code here error(0); return 0; } 

string GetToken() { string token; char ch; // Write the code here. Read the next token and store it in variable "token". // The token must be read character by character. Use the regular expression // defined above to extract tokens from the input. // // To read a character from keyboard, use: // //cin.get(ch); // // where "ch" is a character variable. //string error; bool inputToken = true; while (inputToken == true) { cin.get(ch); while (ch == ' ') { cin.get(ch); } if (isdigit(ch)) { while (isdigit(ch)) { token += ch; cin.get(ch); if (ch == '.') { token += ch; cin.get(ch); } if (ch == ';') token = token + ' ' + ch; if (ch == '#') { token = token + ' ' + ch + ':' + " Error: Unrecognizable token"; //error(isdigit(ch)); inputToken = false; } } inputToken = false; } else { token += ch; if (token == "i") inputToken = true; else if (token == "in") inputToken = true; else if (token == "int") inputToken = false; else if (token == "f") inputToken = true; else if (token == "fl") inputToken = true; else if (token == "flo") inputToken = true; else if (token == "floa") inputToken = true; else if (token == "float") inputToken = false; else if (token == "A" || token == "B" || token == "C" || token == "D" || token == "E") inputToken = false; else if (token == "=") inputToken = false; else if (token == ";") inputToken = false; else if (token == " ") { token = ""; inputToken = false; } } } return token; } 

 void error(int code) { switch (code) { case 0: cout << "no errors found" << endl; break; case 1: cout << "unrecognizable type" << endl; break; case 2: cout << "illegal variable name" << endl; break; case 3: cout << "unexpected number" << endl; break; case 4: cout << "; expected" << endl; } return; }