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Program to Construct a recursive descent parser for an expression.

Program to Construct a recursive descent parser for an expression.

Agenda
1.Algorithm
2.Code(program)
3.Input/output

1.Algorithm

Read the input string.
Write procedures for the non terminals
Verify the next token equals to non terminals if it satisfies match the non terminal.
If the input string does not match print error.

2.Code

#include<stdio.h>

#include<conio.h>

#include<string.h>

char input[100];

int i, l;

void main()
{

  clrscr();
printf("\nRecursive descent parsing for the following grammar\n");
  printf("\nEnter the string to be checked:");
  gets(input);
if (E())

  {

    if (input[i + 1] == '\0')

      printf("\nString is accepted");

    else

      printf("\nString is not accepted");

  } else

    printf("\nString not accepted");

  getch();

}

E()

{

  if (T())

  {

    if (EP())

      return (1);

    else

      return (0);

  } else

    return (0);

}

EP()

{

  if (input[i] == '+')

  {

    i++;

    if (T())

    {

      if (EP())

        return (1);

      else

        return (0);

    } else

      return (0);

  } else

    return (1);

}

T()

{

  if (F())

  {

    if (TP())

      return (1);

    else

      return (0);

  } else

    return (0);

}

TP()

{

  if (input[i] == '*')

  {

    i++;

    if (F())

    {

      if (TP())

        return (1);

      else

        return (0);

    } else

      return (0);

  } else

    return (1);

}

F()

{

  if (input[i] == '(')

  {

    i++;

    if (E())

    {

      if (input[i] == ')')

      {

        i++;

        return (1);

      } else

        return (0);

    } else

      return (0);

  } else if (input[i] >= 'a' && input[i] <= 'z' || input[i] >= 'A' && input[i] <= 'Z')

  {

    i++;

    return (1);

  } else

    return (0);

}


3.Input/Output

Recursive descent parsing for the following grammar

E->TE'

E'->+TE'/@

T->FT'

T'->*FT'/@

F->(E)/ID

Enter the string to be checked:(a+b)*c

String is accepted

Recursive descent parsing for the following grammar

E->TE'

E'->+TE'/@

T->FT'

T'->*FT'/@

F->(E)/ID




Enter the string to be checked:a/c+d

String is not accepted


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