Write a C program for constructing recursive descent parsing.

Code:

#include<stdio.h>

int flag=0;

char l;

void E();

void match(char t) {

if(l==t)

l=getchar();

else

printf("ERROR!");

}

void F() {

if(l>='a' && l<='z')

match(l);

else if(l==‘(') {

match('(');

E();

l=getchar();

}

else

flag=1;

}

void T1() {

if(l==‘*') {

match('*');

F();

T1();

}

else

return;

}

void T() {

F();

T1();

} void E1() {

if(l==‘+') {

match('+');

T();

E1();

}

else {return;}

}

void E() {

T();

E1();

}

int main() {

printf("\nE->E+T|T\n");

printf("\nT->T*F|F\n");

printf("\nF->(E)|i\n\n");

printf("ENTER THE INPUT STRING :-\n");

l=getchar();

E();

if(l=='$' && flag==0)

printf("\nPARSING COMPLETED !!\n ENTER STRING IS CORRECT\n");

else

printf("ERROR!!!");

return 0;

}

Input & Output :

[root@SAR085 Desktop]# gcc sp_7.c

[root@SAR085 Desktop]# ./a.out

E->E+T|T

T->T*F|F

F->(E)|i

1.

ENTER THE INPUT STRING :-

a*b*c$

PARSING COMPLETED !!

ENTER STRING IS CORRECT

2.

ENTER THE INPUT STRING :-

a**a

ERROR!!!