Question

Syntax checker. We will write C code to check to see if an input string can be derived from a grammar. The grammar is:

A ::= 0 B

B ::= 1 A | 2 B | ;

Your program "check.c" should output "yes" if the line of standard input can be derived from this grammar, and "no" otherwise. Here are some examples:

$ ./check

0 ;

yes

$ ./check

0 2 1 ;

no

$

The input values will always be separated by spaces, as shown above. Only edit the file where at the comments 'YOUR CODE HERE'.  

******************** check.c ************************

#include <stdio.h>
#include <string.h>

// Instructions:
// Edit the code below ONLY at the comments showing YOUR CODE HERE.

// Hints:
// You may need additional scanf() statements, but they can be just
// like the scanf() statements already in the code below.

// check whether the input can be derived from this grammar
// A ::= 0 B
// B ::= 1 A | 2 B | ;

int A(), B();

int A() {
int n;
char tok[10];

// read a string from input
n = scanf("%s", &tok);

// YOUR CODE HERE

}

int B() {
int n;
char tok[10];

n = scanf("%s", &tok);

// YOUR CODE HERE

}

int main() {
A();
}

Answer 1

#include <stdio.h>
#include <string.h>

int A(), B();

int A() {
int n;
char tok[10];

// read a string from input
n = scanf("%s", &tok);

// YOUR CODE HERE
//first character should be 0
if(strcmp(tok,"0")==0)
{
   B();
}
else printf("no");
}

int B() {
int n;
char tok[10];

n = scanf("%s", &tok);

// YOUR CODE HERE
//if next character is 2 then call B()
if(strcmp(tok,"2")==0)
{
   B();
}
else if(strcmp(tok,"1")==0) //if next character is 1 then call A()
{
   A();
}
else if(strcmp(tok,";")==0) //if next character is ; then print yes
{
   printf("yes");
}
else printf("no");
}

int main() {
A();
}

output:

0 1 0 2 2 1; yes Process exited after 14.74 seconds with return value 3 Press any key to continue - -