CodeProject
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| Sample Output when syntax is correct |
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>
#define MAX 100
#define ID 261 //identifier
#define ARRAY 262 //array
#define COMMA 265 //','
#define SMCOLON 266 //';'
#define PNTR 267 //pointer
#define OBRCS 268 //'{'
#define CBRCS 269 //'}'
#define INVALID 270 //not a
valid type for our tokens
#define FAILURE 0
#define SUCCESS 1
//this program will now detect Structure declaration like " struct abc{int a,*v,p[]; float e,*o,y[]; char
r,*t,w[];}; "
//grammer:
// str_stmt -> struct
sname{ dec_list };
// dec_list -> dec_stmt
rest_stmts
// rest_stmts -> dec_stmt
rest_stmts | NULL
// dec_stmt -> type
var_list;
// type -> int
| float | char
// var_list -> var
rest_list
// rest_list -> ,
var_list | NULL
// sname -> ID
// var -> ID
// |ARRAY
// |PNTR
char str[MAX]; //our input string
char token[MAX]; //contains a token
int token_type; //the type of token
char *s; //pointer to str
void get_token(); //function to get next token
int str_stmt(); //struct statement
int dec_list(); //declaration of struct members
int rest_stmts(); //rest of dec_stmts if there
int dec_stmt(); //function to verify declaration syntax
int type(); //function to check type
int var_list(); //function to check varaible syntax
int rest_list(); //fuction to check variable list,rest_list and var_list
work recursively and call each other
int main()
{
while(1)
{
s=str;
printf("\nENTER DECLARTATION SYNTAX: ");
gets(s);
if( str_stmt() )
printf("\n\n***** SYNTAX CORRECT *****\n\n");
else
printf("\n\n***** SYNTAX INCORRECT *****\n\n");
}
return 0;
}
int str_stmt()
{
get_token();
if(strcmp(token,"struct")
== 0)
{
printf("\tMATCHED KEYWORD
: %s",token);
get_token();
if(token_type == ID)
{
printf("\tMATCHED IDENTIFIER : %s",token);
get_token();
if(token_type == OBRCS)
{
printf("\tMATCHED OBRCS
: %s",token);
if(dec_list())
return SUCCESS;
}
else
printf("\tExpecting '{'");
}
else
printf("\tExpecting struct name.");
}
else
printf("\tExpecting struct keyword");
return FAILURE;
}
int dec_list()
{
get_token();
if(dec_stmt())
{
printf("\n\t\t\t\t\t-> MATCHED DEC_STMT");
if(rest_stmts())
return SUCCESS;
}
else
printf("\n\t\t\t\t\t-> DEC_STMT INCORRECT");
return FAILURE;
}
int rest_stmts()
{
get_token();
if(token_type == CBRCS)
{
printf("\tMATCHED CBRCS
: %s",token);
get_token();
if(token_type == SMCOLON)
{
printf("\tMATCHED SMCOLON
: %s",token);
return SUCCESS;
}
else
printf("\tExpecting ';'");
}
else if(dec_stmt())
{
printf("\n\t\t\t\t\t-> MATCHED DEC_STMT");
if(rest_stmts())
return SUCCESS;
}
else
printf("\n\t\t\t\t\t->Expecting valid dec_stmt or
'}'.");
return FAILURE;
}
int dec_stmt()
{
if( (strcmp(token,"int")
== 0) ||(strcmp(token,"float") ==
0) || (strcmp(token,"char") == 0)
)
{
printf("\tMATCHED TYPE
: %s",token);
if(var_list() )
return SUCCESS;
}
else
printf("\tExpecting correct TYPE");
return FAILURE;
}
int var_list()
{
get_token();
if(token_type == ID)
{
printf("\tMATCHED IDENTIFIER : %s",token);
if( rest_list() )
return SUCCESS;
}
else if(token_type ==
ARRAY)
{
printf("\tMATCHED ARRAY-ID
: %s",token);
if( rest_list() )
return SUCCESS;
}
else if(token_type ==
PNTR)
{
printf("\tMATCHED POINTER
: %s",token);
if( rest_list() )
return SUCCESS;
}
else
printf("\tExpecting an ID, POINTER or ARRAY");
return FAILURE;
}
int rest_list()
{
get_token();
if(token_type == COMMA)
{
printf("\tMATCHED COMMA
: %s",token);
if( var_list() )
return SUCCESS;
}
else if(token_type ==
SMCOLON)
{
printf("\tMATCHED SMCOLON
: %s",token);
return SUCCESS;
}
else
printf("\tExpecting ',' or ';'");
return FAILURE;
}
void get_token()
{
//before writing this function, remember this is the base
of whole program
//have in mind what we need : ID ARRAY ( ) , ; =
//rest are invalid for our needs right now
char* tostr_tt(int
token_type);
int i = 0; //index for token string
while(*s == ' ' ||
*s == '\t') //eat white spaces
s++;
if(*s == '*') //pointer
{
token[i++]
= *s++;
if(isalpha(*s) || *s == '_')
{
token_type=PNTR;
while(isalnum(*s) || *s == '_') //while token is a
valid ID
token[i++]
= *s++;
}
else
token_type=INVALID;
token[i]
= '\0';
}
else if( isalpha(*s)
|| *s == '_') //if current token starts with an
alphaber or _ it is an ID
{
token_type=ID;
while(isalnum(*s) || *s == '_') //while token is a
valid ID
{
token[i++]
= *s++;
}
token[i]
= '\0';
}
else
{
if(*s == ',')
token_type
= COMMA;
else if(*s == ';')
token_type
= SMCOLON;
else if(*s == '{')
token_type
= OBRCS;
else if(*s == '}')
token_type
= CBRCS;
else
token_type
= INVALID;
token[i++]
= *s++;
token[i]
= '\0';
}
if(token_type == ID) //array is ID[]
{
if(*s == '[')
{
token_type
= INVALID;
token[i++]
= '[';
s++;
if(*s == ']')
{
token_type
= ARRAY;
token[i++]
= ']';
s++;
}
token[i]
= '\0';
}
}
printf("\nTOKEN : %s\t\tTYPE:%-10s",token,tostr_tt(token_type));
}
char* tostr_tt(int
token_type)
{
switch(token_type)
{
case ID: return "ID"; break;
case ARRAY: return "ARRAY"; break;
case COMMA: return "COMMA"; break;
case SMCOLON: return "SMCOLON"; break;
case PNTR: return "POINTER"; break;
case OBRCS: return "OBRACES"; break;
case CBRCS: return "CBRACES"; break;
case INVALID: return "INVALID"; break;
default: return "ERROR"; break;
}
}
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