Question

Implement Lexer(Scanner) that scans the whole source code entered by the user that includes Alphabets(characters), integers(digits), operators(arithmatic, logical and relational operators), and special symbols. output should be in the form of Symbol table that shows each token with its name, type and number of times entered(lexexmes). dictionary should be implemented in the code by writing RegX for each category. code entered from internet will be discarded. Implementation language will be of your own choice.

I really need the answer of this question, if someone can do that i would really appreciate it.

Answer 1

When an identifier in the source program is detected by the lexical analyzer, the identifier is entered into the symbol table.

A symbol table is a data structure containing a record for each identifier, with fields for the attributes of the identifier. The data structure allows us to find the record for each identifier quickly and to store or retrieve data from that record quickly.

Code:

function lexan : integer;

var lexbuf : array[0...100] of char;

c : char;

begin

loop begin

read a character into c;

if c is a blank or a tab then

do nothing

else if c is a newline then

lineno := Iineno + I

else if c is a digit then begin

set tokenval to the value of this and following digits;

return NUM

end

elseif c is a letter then begin

place c and successive letters and digits into  lexbuf;

p := lookup(lexbuf);

if p=0 then

p := insert(lexbuf,ID);

tokenval := p

return the token field of table entry p ;

end

else begin /* token is a single character */

set tokenval to NONE; /*there is no attribute */

  return integer ending of character c

end

end

end