Question

Compiler Design

Please help me with this lexical analysis In C

Using FInite automata and a driver.

With file test scanner , main, scanner, token.h

• All case sensitive
• Each scanner error should display "Scanner Error:" followed by details including the line number ff available
• Alphabet
  • all English letters (upper and lower), digits, plus the extra characters as seen below, plus WS
  • No other characters allowed and they should generate errors
• Identifiers
  • begin with a lower case letter and
  • continue with any number of letters or underscores
  • you may assume no identifier is longer than 8 characters
• Keywords (reserved, suggested individual tokens)
• Operators and delimiters group.
• Integers
  • any sequence of decimal digits, no sign, no decimal point
  • you may assume no number longer than 8 characters
• Comments start with $ and end with $

Answer 1

/* Program to implement lexical analyser in C.

Store the inputs in a file "input.txt"in the same location

where this program is saved.

*/

#include<stdio.h>

#include<string.h>

#include<ctype.h>

int isKeyword(char buffer[]) //function to check if the string is keyword

{

char keywords[32][10] = {"auto","break","case","char","const","continue","default",

"do","double","else","enum","extern","float","for","goto",

"if","int","long","register","return","short","signed",

"sizeof","static","struct","switch","typedef","union",

"unsigned","void","volatile","while"};

int i, flag = 0;

for(i = 0; i < 32; ++i)

{

if(strcmp(keywords[i], buffer) == 0)

{

flag = 1; //if string matches with any keyword

break;

}

}

return flag;

}

void main() //main function

{

char ch, buffer[15], operators[] = "+-*/%=";

FILE *fp; //fp is the file pointer used to open file

int i,j=0;

clrscr();

fp = fopen("inputfile.txt","r"); //opening input file

if(fp == NULL) //no such file exists

{

printf("\n\t Error while opening the file");

exit(0);

}

while((ch = fgetc(fp)) != EOF)

{

for(i = 0; i < 6; ++i)

{

if(ch == operators[i])

printf("\n\t %c is operator",ch);

}

if(isalnum(ch))

{

buffer[j++] = ch;

}

else if((ch == ' ' || ch == '\n') && (j != 0))

{

buffer[j] = '\0';

j = 0;

if(isKeyword(buffer) == 1)

printf("\n\t %s is Keyword",buffer);

else

printf("\n\t %s is Indentifier",buffer);

}

}

fclose(fp); //closing the input file

getch();

}