C Program to implement Recursive Descentive Parsing.

#include

#include

#include

#include

#include

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->E+T/T \n\t\t T->T*F/F \n\t\t F->(E)/Id ");

 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();

}