Concepts of Programming Languages

Instructions: Make the attached parser program work in C++. Show me the cpp file, successful compilation, and a picture of the output screen.

/* front.c - a lexical analyzer system for simple

arithmetic expressions */

#include

#include

/* Global declarations */

/* Variables */

int charClass;

char lexeme [100];

char nextChar;

int lexLen;

int token;

int nextToken;

FILE *in_fp, *fopen();

/* Function declarations */

void addChar();

void getChar();

void getNonBlank();

int lex();

/* Character classes */

#define LETTER 0

#define DIGIT 1

#define UNKNOWN 99

/* Token codes */

#define INT_LIT 10

#define IDENT 11

#define ASSIGN_OP 20

#define ADD_OP 21

#define SUB_OP 22

#define MULT_OP 23

#define DIV_OP 24

#define LEFT_PAREN 25

#define RIGHT_PAREN 26

/******************************************************/

/* main driver */

main() {

/* Open the input data file and process its contents */

if ((in_fp = fopen("front.in", "r")) == NULL)

printf("ERROR - cannot open front.in ");

else {

getChar();

do {

lex();

} while (nextToken != EOF);

}

}

/*****************************************************/

/* lookup - a function to lookup operators and parentheses

and return 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 = MULT_OP;

break;

case '/':

addChar();

nextToken = DIV_OP;

break;

default:

addChar();

nextToken = EOF;

break;

}

return nextToken;

}

/*****************************************************/

/* addChar - a function to add nextChar to lexeme */

void addChar() {

if (lexLen <= 98) {

lexeme[lexLen++] = nextChar;

lexeme[lexLen] = 0;

}

else

printf("Error - lexeme is too long ");

}

/*****************************************************/

/* getChar - a function to get the next character of

input and determine its character class */

void getChar() {

if ((nextChar = getc(in_fp)) != EOF) {

if (isalpha(nextChar))

charClass = LETTER;

else if (isdigit(

nextChar))

charClass = DIGIT;

else charClass = UNKNOWN;

}

else

charClass = EOF;

}

/*****************************************************/

/* getNonBlank - a function to call getChar until it

returns a non-

whitespace

character */

void getNonBlank() {

while (isspace(nextChar))

getChar();

}

/

*****************************************************/

/* lex - a simple lexical analyzer for arithmetic

expressions */

int lex() {

lexLen = 0;

getNonBlank();

switch (charClass) {

/* Parse identifiers */

case LETTER:

addChar();

getChar();

while (charClass == LETTER || charClass == DIGIT) {

addChar();

getChar();

}

nextToken = IDENT;

break;

/* Parse integer literals */

case DIGIT:

addChar();

getChar();

while (charClass == DIGIT) {

addChar();

getChar();

}

nextToken = INT_LIT;

break;

/* Parentheses and operators */

case UNKNOWN:

lookup(nextChar);

getChar();

break;

/* EOF */

case EOF:

nextToken = EOF;

lexeme[0] = 'E';

lexeme[1] = 'O';

lexeme[2] = 'F';

lexeme[3] = 0;

break;

} /* End of switch */

printf("Next token is: %d, Next lexeme is %s ",

nextToken, lexeme);

return nextToken;

} /* End of function lex */

The results:

Next token is: 25 Next lexeme is (

Next token is: 11 Next lexeme is sum

Next token is: 21 Next lexeme is +

Next token is: 10 Next lexeme is 47

Next token is: 26 Next lexeme is )

Next token is: 24 Next lexeme is /

Next token is: 11 Next lexeme is total

Next token is: -1 Next lexeme is EOF