Lexical Analyser

23. Program to implement Lexical Analyser?

Program

#include<conio.h>

#include<stdio.h>

void findtokens();

int i,n,x=0,y=0,q=0,w=0,p,flag,j,k=0,a=0,b,o;

char c,str[20],delm[20]={',',';','{','}','(',')'},opr[20]="<>'+-*/=&",string[20],oprf[20],keys[20][20],ids[20][20],spl[20],stringf[20],keyw[20][20]={"int","void","float","char","if","else","printf","scanf"},cons[20],constr[20];

void display();

void main()

{

            FILE *f1;

            clrscr();

            printf(“The Input:\n”);

            /*------Input the program to be evaluated into the file pgm.txt------*/

            f1=fopen("z:\\pgm.txt","r");

            while((c=getc(f1))!=EOF)

            {            printf("%c" ,c);

            }

            fclose(f1);

            findtokens();

            display();

            getch();

}

void display()

{

                        /*------Displaying all the arrays-----*/

                        printf(" \nOperators : %s ",oprf);

                        printf("\nSpecial Characters : %s " ,spl);

                        printf("\nKeywords :");

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

                                    printf(" %s",keys[i]);

                        printf("\nIdentifiers :");

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

                                    printf(" %s",ids[i]);

                        printf("\nStrings :");

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

                                    printf("%c",stringf[i]);

                        printf("\nConstants : %s",constr );

}

/*----Finding and separating tokens into different arrays----*/

void findtokens()

{

            int flag2,z;

            FILE *f1;

            i=0;

            f1=fopen("z:\\pgm.txt","r");

            while((c=getc(f1))!=EOF)

            {

                        flag=0;

                        flag2=0;

                        /*-----Storing operators in to the array oprf[]----*/

                        for(j=0;opr[j]!='\0';j++)

                                    if(c==opr[j])

                                    {

                                                flag=1;

                                                for(z=0;z<k;z++)

                                                            if(c==oprf[z])

                                                                         flag2=1;

                                                if(flag2==0)

                                                {

                                                            oprf[k]=c;

                                                            k++;

                                                }

                                    }

                        /*----Storing special characters into the array spl[]----*/

                        for(j=0;delm[j]!='\0';j++)

                                                if(c==delm[j])

                                                {

                                                            flag=1;

                                                            for(z=0;z<q;z++)

                                                                        if(c==spl[z])

                                                                                    flag2=1;

                                                            if(flag2==0)

                                                            {

                                                                        spl[q]=c;

                                                                        q++;

                                                            }

                                                }

                   /*-----Storing strings into the array stringf[]-----*/

                   if(c=='"')

                   {

                                    c=getc(f1);

                                    while(c!='"')

                                    {

                                                stringf[w]=c;

                                                            w++;

                                                c=getc(f1);

                                    }

                                    stringf[w]=' ';

                                    w++;

                                    flag=1;

                   }

/*----Storing constants into the array constr[]----*/

                   if((flag==0)&&(c!=' ')&&(c!='\n')&&(c!='\t' ))

                         {

                                    if(isdigit(c)!=0)

                                    {

                                                cons[b]=c;

                                                b++;

                                    }

                                    else

                                                b=0;

                                    string[i]=c;

                                    i++;

                        }

                        else

                        {

                             if((b!=0)&&(i==b))

                             {

                                    for(o=0;o<b;o++)

                                                constr[a++]=cons[o];

                                    constr[a++]=' ';

                                    b=0;

                             }

                             else

                             if(i!=0)

                                         {

                                                flag=0;

                                                 string[i]='\0';

                                                if(strcmp(string,"#include")==0)

                                                {

                                                            while(c!='\n')

                                                                        c=getc(f1);

                                                            k--;

                                                }

                                    /*----Storing keywords into the array keys[]----*/

                                                else

                                                {

                                                 for(p=0;p<=7;p++)

                                                            if(strcmp(string,keyw[p])==0)

                                                                        flag=1;

                                          if(flag==1)

                                                {

                                                            flag2=0;

                                                                         for(z=0;z<x;z++)

                                                                                    if(strcmp(keys[z],string)==0)

                                                                                                flag2=1;

                                                                         if(flag2==0)

                                                                {                  strcpy(keys[x],string);

                                                            x++;

                                                            }

                                                }

                                    /*----Storing identifiers into the array ids[]----*/

                                                else

                                                {

                                                            if((string[0]=='_')||(isalpha(string[0])!=0))

                                                            {       flag=1;

                                                                        for(i=0;string[i]!='\0';i++)

                                                                                   if((isalnum(string[i])==0)&&(string[i]!='_'))

                                                                                                flag=0;

                                                            }

                                                            if(flag==1)

                                                             {       flag2=0;

                                                                         for(z=0;z<y;z++)

                                                                                    if(strcmp(ids[z],string)==0)

                                                                                                flag2=1;

                                                                         if(flag2==0)

                                                                         {

                                                                                     strcpy(ids[y],string);

                                                                                     y++;

                                                                         }

                                                             }

                                                }

                                                }

                                                i=0;

                                                b=0;

                                         }

                                        }

                                    }

                        oprf[k]='\0';

                                    spl[q]='\0';

                                    constr[a]='\0';

}

Output

The Input:

#include<stdio.h>

void main()

{

int a,b;

a=b+5;

printf(“sum=”,%a);

}

Operators :

+

=

Special characters :

(

)

{

,

;

}

Keywords :

void

int

printf

Identifiers :

main

a

b

Strings :

sum=

Constants :

5