Experiment no 1

Problem Statement    : Write a program in C/Cpp to identify keywords, identifiers and special symbols in a given program.

Methodology:

1. Create a c program.

2. Open the *.c file/program in the read mode

3. Identify keywords, identifiers and special symbols and store them in appropriate data structure

4. Display each data structure i.e. keywords, identifiers and special symbols.

Theory            :

                        In the fundamentals of language processing we know there are two steps analysis  and synthesis as,

Language processing= Analysis of Source program + Synthesis of target program.

The first operand, The Analysis of source program, consists of three components as

i) Lexical Analysis

ii) Syntax Analysis

iii) Semantic Analysis

The lexical analysis identifies the operators, constants and identifiers. Let us take an example to see how a lexical units are formed by the lexical analysis.

e.g.                     percent_profit=(profit*100)/cost_price;

In the above statement lexical analysis identifies

i)  = , * ,  /  as operators

ii)100 as constant

iii) percent_profit , profit & cost_price as identifiers.

Keywords:

                        In the program there are some words which has special meaning already defined in the compiler , called keywords.

e.g. int, char, if , goto etc.

Identifiers:

                        Identifiers are the lexical tokens we can call these as variables. There are some rules to define the variable. Hence some variables are listed as follows:

e.g. int a,b,c; 

In the above example a, b, c are three variables.

Special Symbols:

                        There may be some symbols present in the statement, there may be

i) *,/,+,- which are used in the program as a operator.

ii) ; to end the statement( except if, else, for etc) etc.

For the lexical analysis we have a *.c program as follows:

void main()

{

int a;

char b;

float c;

}

In the above program we can see that there are three data types int, char & float along with a, b, c as identifiers.

The program will give the following output:

Keywords are int, char, float

Identifiers are a,b,c

Symbols are , ;;;

Frequently asked questions:

      1. What is mean by language processor? 

      2. What is the difference between analysis and synthesis?.

3.  What is mean lexical analysis?  

4.  Write down different keywords, identifiers and symbols used in the program.

CODE:

input files:

1. IN.txt

ADD BREG,C
MOVE AREG,A
MOVE BREG,B
SUB AREG,B
ADD BREG,='10'

2. KEY_IN.txt

MOVE
ADD
SUB
MUL

3.REG_IN.txt

AREG
BREG
CREG
DREG

4. MAIN program

#include<conio.h>
#include<iostream.h>
#include<string.h>
#include<fstream.h>
#include<stdlib.h>
# define MAX 80
# define SI 30
void main()
{
char str[SI],str1[SI],str2[SI],strc[SI];
clrscr();
fstream f,f1,f2,f3;
f.open("sp\\in.txt",ios::beg|ios::in);
while(f.getline(str,MAX))
{
  strcpy(strc,str);
  strcpy(str1,strtok(str," "));
  f1.open("sp\\key_in.txt",ios::beg|ios::in);
  while(f1.getline(str,MAX))
  {
     if(strcmp(str,str1)==0)
     {
    cout<<"\n"<<str<<"is Memonics";
    break;
      }
  if(f1.eof())
  break;
  }
  f1.close();
   strcpy(str,strc);
   strcpy(str,strtok(str," "));
   strcpy(str,strtok(NULL," "));
   strcpy(str2,strtok(str,","));
   f1.open("sp\\reg_in.txt",ios::beg|ios::in);
  while(f1.getline(str1,MAX))
  {
     if(strcmp(str1,str2)==0)
     {
    cout<<"\n"<<str<<"is Register";
    break;
      }
    if(f1.eof())
  break;
  }
  f1.close();
  strcpy(str,strc);
   strcpy(str,strtok(str," "));
   strcpy(str,strtok(NULL," "));
   strcpy(str2,strtok(str,","));
  strcpy(str2,strtok(NULL,","));
  if(!strstr(str2,"="))
  {
    cout<<"\n"<<str2<<"is Symbol";
  }
   else
    cout<<"\n"<<str2<<"is Literal";
  if(f.eof())
  break;
}
f.close();
getch();
}