Question

Write a Lexical analyzer (in C) to identify: parenthesis, exponents, multiplication,division, addition, subtraction, assignment ("==") and inequality ("!=").

Please make sure to use C language.

Answer 1

Lexical analysis is done by compiler. It is the first phase. The compiler coverts the progrsm into a sequence of tokens. We know that token is the smallest unit in a program such as variables, keywords, constants, special characters etc. Lexical analyzer removes the white space characters and seperates each tokens from the program without including commented statements. And it checks for the error and returns the row and column number of the error. Check for the following program:

#include<stdio.h>

#include<conio.h>

void main()

{

char str[2]; // is a character array which can store only two //characters.. This for reading operator from the user.

printf("\n Enter the operator:") ;

gets(str);

/*reading operator, if the operator is a single operator like +,-,* then it stores in str[0] and for double character like ==, != the second character stores in str[1] position.*/

switch(str[0]) //checking case value, str[0] retrieves the first //character as operator

{

case '(': // case checking for open bracket

printf("\n Open parathesis");//if it is true print the statement

break;

case ')': //case checking for closed bracket, if it is true, then //print the statement

printf("\n Closed parathesis");

break;

case '^': //checking for exponents

printf("\nExponents"); // if case operator true, then print the //statement

break;

case '*': //checking for *

printf("\nMultiplication");

break

case '/': //checking for division operator

printf("\nDivision");

break;

case '+': // checking for addition operator

printf("\nAddition");

break;

case '-': //checking for subtraction

printf("\n Subtraction");

break; // exiting from switch

case '=': // checking for =

if(str[1]=='=')

/* checking for ==. Here, str[0] stores the first = and str[1] stores the second =. If it is true then print ==*/

printf("\nEqual to equal to");

else. //otherwise only =

printf("\nEqual to or Assignment");

break;

case '!': //check for !=. If str[0]is eqal to ! and str[1] is equal to = //then prints not eqal to otherwise equal to.

if(str[1]=='=')

printf("Not eqal to");

else

printf("eual to");

break; // exiting from switch.

default: // if enter an operator other than the operators in case //values execute the below statemebt

printf("Invalid operator");

break;

}

getch();

}