i am having issues correcting an error in my program here is my code: #include <iostream>...
i am having issues correcting an error in my program
here is my code:
#include <iostream> // define libraries
#include <fstream>
using namespace std;
// Variable definitions:
ifstream infp; // file handler
enum Tokens {INT_LIT, IDENT, ASSIGN_OP, ADD_OP, SUB_OP, MUL_OP, DIV_OP, LEFT_PAREN, RIGHT_PAREN, LETTER, DIGIT, UNKNOWN,ENDFILE};
Tokens nextToken; // nextToken read from the file.
int charClass; // char class
char lexeme [100]; // number of characters per line
char nextChar; // next char read from the file
int lexLen; // number of characters in lexeme so far.
// function to get the next character from the file
void getChar()
{
if ((nextChar = infp.get()) != EOF)
{
if (isalpha(nextChar)) charClass = LETTER;
else if (isdigit(nextChar)) charClass = DIGIT;
else charClass = UNKNOWN;
}
else charClass = ENDFILE;
}
// function to skip all white spaces
void skipWhiteSpace()
{
while (isspace(nextChar))
getChar();
}
// function add the character read from the file into the arraylexeme
void addChar()
{
if (lexLen < 99)
{
lexeme[lexLen++] = nextChar;
lexeme[lexLen] = 0;
}
else cout << "Error - lexeme is too long \n";
}
// function to determine the token
int lookup(char ch)
{
switch (ch)
{
case '(': addChar(); nextToken = LEFT_PAREN; break;
case ')': addChar(); nextToken = RIGHT_PAREN; break;
case '+': addChar(); nextToken = ADD_OP; break;
case '-': addChar(); nextToken = SUB_OP; break;
case '*': addChar(); nextToken = MUL_OP; break;
case '/': addChar(); nextToken = DIV_OP; break;
case '=': addChar(); nextToken = ASSIGN_OP; break;
default: addChar(); nextToken = ENDFILE; break;
}
return nextToken;
}
void print(Tokens t)
{ // print out the token category.
switch (t)
{
case INT_LIT: cout << "<INT_LIT>"; break;
case IDENT: cout << "<IDENT>"; break;
case ASSIGN_OP: cout << "<ASSIGN_OP>"; break;
case ADD_OP: cout << "<ADD_OP>"; break;
case SUB_OP: cout << "<SUB_OP>"; break;
case MUL_OP: cout << "<MUL_OP>"; break;
case DIV_OP: cout << "<DIV_OP>"; break;
case LEFT_PAREN: cout << "<LEFT_PAREN>"; break;
case RIGHT_PAREN: cout << "<RIGHT_PAREN>"; break;
case LETTER: cout << "<LETTER>"; break;
case DIGIT: cout << "<DIGIT>"; break;
case UNKNOWN: cout << "<UNKNOWN>"; break;
case ENDFILE: cout << "<ENDFILE>"; break;
} /* End of switch */
} /* End of function print */
int lex()
{ //function lex() returns a token for each lexeme read from the file
lexLen = 0; skipWhiteSpace();
switch (charClass)
{
case LETTER:
while (charClass == LETTER || charClass == DIGIT)
{
addChar();
getChar();
}
nextToken = IDENT;
break;
case DIGIT:
while (charClass == DIGIT)
{
addChar();
getChar();
}
nextToken = INT_LIT;
break;
case UNKNOWN: lookup(nextChar);
nextChar = ' ';
break;
case ENDFILE:
nextToken=ENDFILE;
lexeme[0]='E';
lexeme[1]='O';
lexeme[2] = 'F';
lexeme[3] = 0;
break;
} /* End of switch */
cout << "Next token is: "; print(nextToken);
cout <<" Next lexeme is " << lexeme << endl;
return nextToken;
} /* End of function lex */
int main() {
infp.open("front.in");
if (!infp) cout << "ERROR - cannot open front.in \n";
else {
nextChar = ' ';
lex();
do {
expr();
} while (nextToken != EOF);
}
return 0;
}
/* Function expr
Parses strings in the language generated by the rule:
<expr> → <term> {(+ | -) <term>}
equivalent to:
<expr> → <term> | <term + <term> | <term> - <term>
*/
void expr() {
printf("Enter <expr>\n");
term(); // Parse the first term
/* As long as the next token is + or -, call lex to get the next token
and parse the next term */
while (nextToken == ADD_OP || nextToken == SUB_OP){
lex();
term();
}
printf("Exit <expr>\n");
}
/* Function: term(): Parses strings in the language generated by the rule:
<term> -> <factor> {(* | /) <factor>} or equivalent to:
<term> -> <factor> | * <factor> | / <factor>
*/
void term() {
printf("Enter <term>\n");
factor(); // Parse the first factor
/* As long as the next token is * or /, next token and parse the next
factor */
while (nextToken == MUL_OP || nextToken == DIV_OP) {
lex();
factor();
}
printf("Exit <term>\n");
} /* End of function term */
/* Function factor: Parses strings generated by the rule:
<factor> -> id | int_constant | (<expr>) */
void factor() {
printf("Enter <factor>\n");
/* Determine which RHS */
if (nextToken) == IDENT || nextToken == INT_LIT)
lex(); /* For the RHS id, just call lex */
else if (nextToken == LEFT_PAREN) {
lex();
expr();
if (nextToken == RIGHT_PAREN)
lex();
else
cout << "Expected ), found " << nextChar << endl;
} /* End of else if (nextToken == ... */
else cout << "Error: Expected (, found " << nextChar << endl;
printf("Exit <factor>\n");
}
Homework Answers
Its compiling perfectly now, wait for the compilation to end and make sure you have front.in file .
#include <iostream> // define libraries
#include <fstream>
using namespace std;
// Variable definitions:
void term();
void expr();
void factor();
ifstream infp; // file handler
enum Tokens {INT_LIT, IDENT, ASSIGN_OP, ADD_OP, SUB_OP, MUL_OP, DIV_OP, LEFT_PAREN, RIGHT_PAREN, LETTER, DIGIT, UNKNOWN,ENDFILE};
Tokens nextToken; // nextToken read from the file.
int charClass; // char class
char lexeme [100]; // number of characters per line
char nextChar; // next char read from the file
int lexLen; // number of characters in lexeme so far.
// function to get the next character from the file
void getChar()
{
if ((nextChar = infp.get()) != EOF)
{
if (isalpha(nextChar)) charClass = LETTER;
else if (isdigit(nextChar)) charClass = DIGIT;
else charClass = UNKNOWN;
}
else charClass = ENDFILE;
}
// function to skip all white spaces
void skipWhiteSpace()
{
while (isspace(nextChar))
getChar();
}
// function add the character read from the file into the arraylexeme
void addChar()
{
if (lexLen < 99)
{
lexeme[lexLen++] = nextChar;
lexeme[lexLen] = 0;
}
else cout << "Error - lexeme is too long \n";
}
// function to determine the token
int lookup(char ch)
{
switch (ch)
{
case '(': addChar(); nextToken = LEFT_PAREN; break;
case ')': addChar(); nextToken = RIGHT_PAREN; break;
case '+': addChar(); nextToken = ADD_OP; break;
case '-': addChar(); nextToken = SUB_OP; break;
case '*': addChar(); nextToken = MUL_OP; break;
case '/': addChar(); nextToken = DIV_OP; break;
case '=': addChar(); nextToken = ASSIGN_OP; break;
default: addChar(); nextToken = ENDFILE; break;
}
return nextToken;
}
void print(Tokens t)
{ // print out the token category.
switch (t)
{
case INT_LIT: cout << "<INT_LIT>"; break;
case IDENT: cout << "<IDENT>"; break;
case ASSIGN_OP: cout << "<ASSIGN_OP>"; break;
case ADD_OP: cout << "<ADD_OP>"; break;
case SUB_OP: cout << "<SUB_OP>"; break;
case MUL_OP: cout << "<MUL_OP>"; break;
case DIV_OP: cout << "<DIV_OP>"; break;
case LEFT_PAREN: cout << "<LEFT_PAREN>"; break;
case RIGHT_PAREN: cout << "<RIGHT_PAREN>"; break;
case LETTER: cout << "<LETTER>"; break;
case DIGIT: cout << "<DIGIT>"; break;
case UNKNOWN: cout << "<UNKNOWN>"; break;
case ENDFILE: cout << "<ENDFILE>"; break;
} /* End of switch */
} /* End of function print */
int lex()
{ //function lex() returns a token for each lexeme read from the file
lexLen = 0; skipWhiteSpace();
switch (charClass)
{
case LETTER:
while (charClass == LETTER || charClass == DIGIT)
{
addChar();
getChar();
}
nextToken = IDENT;
break;
case DIGIT:
while (charClass == DIGIT)
{
addChar();
getChar();
}
nextToken = INT_LIT;
break;
case UNKNOWN: lookup(nextChar);
nextChar = ' ';
break;
case ENDFILE:
nextToken=ENDFILE;
lexeme[0]='E';
lexeme[1]='O';
lexeme[2] = 'F';
lexeme[3] = 0;
break;
} /* End of switch */
cout << "Next token is: "; print(nextToken);
cout <<" Next lexeme is " << lexeme << endl;
return nextToken;
} /* End of function lex */
int main() {
infp.open("front.in");
if (!infp) cout << "ERROR - cannot open front.in \n";
else {
nextChar = ' ';
lex();
do {
expr();
} while (nextToken != EOF);
}
return 0;
}
/* Function expr
Parses strings in the language generated by the rule:
<expr> → <term> {(+ | -) <term>}
equivalent to:
<expr> → <term> | <term + <term> | <term> - <term>
*/
void expr() {
printf("Enter <expr>\n");
term(); // Parse the first term
/* As long as the next token is + or -, call lex to get the next token
and parse the next term */
while (nextToken == ADD_OP || nextToken == SUB_OP){
lex();
term();
}
printf("Exit <expr>\n");
}
/* Function: term(): Parses strings in the language generated by the rule:
<term> -> <factor> {(* | /) <factor>} or equivalent to:
<term> -> <factor> | * <factor> | / <factor>
*/
void term() {
printf("Enter <term>\n");
factor(); // Parse the first factor
/* As long as the next token is * or /, next token and parse the next
factor */
while (nextToken == MUL_OP || nextToken == DIV_OP) {
lex();
factor();
}
printf("Exit <term>\n");
} /* End of function term */
/* Function factor: Parses strings generated by the rule:
<factor> -> id | int_constant | (<expr>) */
void factor() {
printf("Enter <factor>\n");
/* Determine which RHS */
if (nextToken == IDENT || nextToken == INT_LIT)
lex(); /* For the RHS id, just call lex */
else if (nextToken == LEFT_PAREN) {
lex();
expr();
if (nextToken == RIGHT_PAREN)
lex();
else
cout << "Expected ), found " << nextChar << endl;
} /* End of else if (nextToken == ... */
else cout << "Error: Expected (, found " << nextChar << endl;
printf("Exit <factor>\n");
}
===========================
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