recursive descent parser in c

Download this file : parse.c




program:

#include"stdio.h"

#include"conio.h"

#include"string.h"

#include"stdlib.h"

#include"ctype.h"

char ip_sym[15],ip_ptr=0,op[50],tmp[50];
void e_prime();
void e();
void t_prime();
void t();
void f();
void advance();
int n=0;
void e()
{
 strcpy(op,"TE'");
 printf("E=%-25s",op);
 printf("E->TE'\n");
 t();
 e_prime();
}

void e_prime()
{
int i,n=0,l;
for(i=0;i<=strlen(op);i++)
    if(op[i]!='e')
tmp[n++]=op[i];
strcpy(op,tmp);
l=strlen(op);
for(n=0;n < l && op[n]!='E';n++);
if(ip_sym[ip_ptr]=='+')
 {
     i=n+2;
do
{
op[i+2]=op[i];
i++;
}while(i<=l);
  op[n++]='+';
  op[n++]='T';
  op[n++]='E';
  op[n++]=39;
  printf("E=%-25s",op);
  printf("E'->+TE'\n");
  advance();
  t();
  e_prime();
 }
 else
 {
     op[n]='e';
  for(i=n+1;i<=strlen(op);i++)
op[i]=op[i+1];
 printf("E=%-25s",op);
 printf("E'->e");
 }
}
void t()
{
int i,n=0,l;
for(i=0;i<=strlen(op);i++)
if(op[i]!='e')
tmp[n++]=op[i];
strcpy(op,tmp);
l=strlen(op);
for(n=0;n < l && op[n]!='T';n++);

i=n+1;
do
{
op[i+2]=op[i];
i++;
}while(i < l);
op[n++]='F';
op[n++]='T';
op[n++]=39;
printf("E=%-25s",op);
printf("T->FT'\n");
f();
t_prime();
}

void t_prime()
{
int i,n=0,l;
for(i=0;i<=strlen(op);i++)
    if(op[i]!='e')
tmp[n++]=op[i];
strcpy(op,tmp);
l=strlen(op);
for(n=0;n < l && op[n]!='T';n++);
if(ip_sym[ip_ptr]=='*')
 {
     i=n+2;
do
{
op[i+2]=op[i];
i++;
}while(i < l);
  op[n++]='*';
  op[n++]='F';
  op[n++]='T';
  op[n++]=39;
  printf("E=%-25s",op);
  printf("T'->*FT'\n");
  advance();
  f();
  t_prime();
 }
 else
 {
   op[n]='e';
  for(i=n+1;i<=strlen(op);i++)
op[i]=op[i+1];
 printf("E=%-25s",op);
 printf("T'->e\n");
 }
}

void f()
{
int i,n=0,l;
for(i=0;i<=strlen(op);i++)
    if(op[i]!='e')
tmp[n++]=op[i];
strcpy(op,tmp);
l=strlen(op);
for(n=0;n < l && op[n]!='F';n++);
 if((ip_sym[ip_ptr]=='i')||(ip_sym[ip_ptr]=='I'))
 {
op[n]='i';
printf("E=%-25s",op);
printf("F->i\n");
advance();
 }
 else
 {
  if(ip_sym[ip_ptr]=='(')
  {
   advance();
   e();
   if(ip_sym[ip_ptr]==')')
   {
    advance();
     i=n+2;
do
{
op[i+2]=op[i];
i++;
}while(i<=l);
  op[n++]='(';
  op[n++]='E';
  op[n++]=')';
  printf("E=%-25s",op);
  printf("F->(E)\n");
   }
  }
  else
  {
   printf("\n\t syntax error");
   getch();
   exit(1);
  }
 }
}

void advance()
{
 ip_ptr++;
}

void main()
{
 int i;
 clrscr();
 printf("\nGrammar without left recursion");
 printf("\n\t\t E->TE' \n\t\t E'->+TE'|e \n\t\t T->FT' ");
 printf("\n\t\t T'->*FT'|e \n\t\t F->(E)|i");
 printf("\n Enter the input expression:");
 gets(ip_sym);
 printf("Expressions");
 printf("\t Sequence of production rules\n");
  e();
  for(i=0;i < strlen(ip_sym);i++)
 {
  if(ip_sym[i]!='+'&&ip_sym[i]!='*'&&ip_sym[i]!='('&&
     ip_sym[i]!=')'&&ip_sym[i]!='i'&&ip_sym[i]!='I')
  {
   printf("\nSyntax error");
   break;
  }
  for(i=0;i<=strlen(op);i++)
    if(op[i]!='e')
tmp[n++]=op[i];
    strcpy(op,tmp);
    printf("\nE=%-25s",op);
 }
 getch();
}

Download this file : parse.c




Output:

Download this file : parse.c

lexical analyser in c

Download this file : lexical


lexical.c

#include"stdio.h"

#include"conio.h"

void main()

{

FILE *fi,*fo,*fop,*fk;

int flag=0,i=1;

char c,t,a[15],ch[15],file[20];

clrscr();

printf("Enter the file name : ");

scanf("%s",file);

fi=fopen(file,"r");

fo=fopen("inter.c","w");

fop=fopen("oper.c","r");

fk=fopen("key.c","r");

c=getc(fi);

while(!feof(fi))

{

if(isalpha(c)||isdigit(c)||(c=='['||c==']'||c=='.'==1))

fputc(c,fo);

else

{

if(c=='\n')

fprintf(fo,"\t$\t");

else

fprintf(fo,"\t%c\t",c);

}

c=getc(fi);

}

fclose(fi);

fclose(fo);

fi=fopen("inter.c","r");

printf("\t\tLEXICAL ANALYSIS \n");

fscanf(fi,"%s",a);

printf("\nline : %d\n",i++);

while(!feof(fi))

{

if((strcmp(a,"$")==0))

{

printf("\nline : %d\n",i++);

fscanf(fi,"%s",a);

}

fscanf(fop,"%s",ch);

while(!feof(fop))

{

if(strcmp(ch,a)==0)

{

fscanf(fop,"%s",ch);

printf("\t\t%s\t:\t%s\n",a,ch);

flag=1;

}

fscanf(fop,"%s",ch);

}

rewind(fop);

fscanf(fk,"%s",ch);

while(!feof(fk))

{

if(strcmp(ch,a)==0)

{

fscanf(fk,"%s",ch);

printf("\t\t%s\t:\tkeyword\n",a);

flag=1;

}

fscanf(fk,"%s",ch);

}

rewind(fk);

if(flag==0)

{

if(isdigit(a[0]))

printf("\t\t%s\t:\tconstant\n",a);

else

printf("\t\t%s\t:\tidentifier\n",a);

}

flag=0;

fscanf(fi,"%s",a);

}

getch();

}

key.c

int

void

main

char

if

for

while

else

printf

scanf

FILE

include

stdio.h

conio.h

iostream.h

oper.c

( openpara

) closepara

{ openbrace

} closebrace

< lesser

> greater

" doublequote

' singlequote

: colon

; semicolon

# preprocessor

= equal

== assign

% percentage

^ bitwise

& reference

* star

+ add

- sub

\ backslash

/ slash

input.c

#include"stdio.h"

#include"conio.h"

void main()

{

int a=10,b,c;

a=b*c;

getch();

}

Download this file : lexical

output:

Enter the file name:input.c

# : preprocessor

include : keyword

< : lesser

stdio.h : keyword

> : greater

line : 2

# : preprocessor

include : keyword

< : lesser

conio.h : keyword

> : greater

line : 3

void : keyword

main : keyword

( : openpara

) : closepara

line : 4

{ : openbrace

line : 5

int : keyword

a : identifier

= : equal

10 : constant

, : identifier

b : identifier

, : identifier

c : identifier

; : semicolon

line : 6

a : identifier

= : equal

b : identifier

* : star

c : identifier

; : semicolon

line : 7

getch : identifier

( : openpara

) : closepara

; : semicolon

line : 8

} : closebrace

Download this file : lexical