/*
** validB.c
**	checking the validity of a given string as an acceptable identifier in C
**  (binary search used)
**   -- written by Jeff Tian, 11/17/98.     
*/

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

#define MaxKeywords 32
#define MaxKeywordLength 12

char get_input(void);
void ignore_line(void);
int IsValidName(char *name);
int IsLiteral(char *name);
int IsKeywordB(char *name);

static char keywords[MaxKeywords][MaxKeywordLength] =
{  
   "auto", "break", "case", "char", "const", "continue", "default", "do",
   "double", "else", "enum", "extern", "float", "for", "goto", "if",
   "int", "long", "register", "return", "short", "signed", "sizeof", "static",
   "struct", "switch", "typedef", "union", "unsigned", "void", "volatile", "while"
};

main()
{
   char c, vname[32];

   printf("This program checks variable/function/constant names for validity.\n");
   c = get_input();
   while (c == 'y' || c == 'Y')
   {
      printf("Please enter a name: ");
      if (IsValidName(vname))                        
         printf("\"%s\" .... is a valid name.\n", vname);
      c = get_input();
   }
}

/*
** get_input() -- query user for continuation and get user input
*/

char get_input(void)
{
   char c;

   printf("\nWould you like to continue [y/n]? ");
   while(isspace(c = getchar()));
   ignore_line();
   return(c);
}

/*
**  ignore_line() -- ignore all the input until '\n'
*/

void ignore_line(void)
{
   while (getchar() != '\n');
}

/*
** IsValidName() -- check validity of names
*/ 

int IsValidName(char *vname)
{
   if (!IsLiteral(vname) )
      return(0);
   if (IsKeywordB(vname) )
      return(0);
   return(1);
}

/*
** IsLiteral() -- check validity of and store alpha-numerical literals
*/ 

int IsLiteral(char *name)
{
   char c; 
   int answer=1, i=0;

   while(isspace(c = getchar()));
   if (!isalpha(c) && c != '_')
   {
      printf("Illegal name: illegal leading character \'%c\'.\n", c);
      answer = 0;
   }

   name[i++] = c;
   c = getchar();
   while (answer && !isspace(c) )
   {
      if (!isalpha(c) && c != '_' && !isdigit(c))
      {
         printf("Illegal name: illegal trailing character \'%c\'.\n", c);
         answer = 0;
      }
      else if (i >= 30)
      {
         printf("Illegal name: string too long.\n");
         answer = 0;
      }
      else
      {
         name[i++] = c;
         c = getchar();
      }
   }

   if (c != '\n') 
      ignore_line();
   name[i] = '\0';
   return(answer);
}

/*
** IsKeywordB() -- check if a given name is a keyword, using binary search
*/ 

int IsKeywordB(char *name)
{
   int i=0, iskywd=0, done=0, lwbd=0, upbd=MaxKeywords-1, order;

   while (!iskywd && !done)
   {
      if (upbd <= lwbd) 
      {
         done = 1;
      }
      else
      {
         i = lwbd + (upbd - lwbd) / 2;
         order = strcmp(keywords[i], name);
         if (order == 0)
         {
            printf("Illegal name: keyword \"%s\" used.\n", name);
            iskywd = 1;
         }
         else if (order < 0)
         {
            lwbd = i+1;
         }
         else
         {
            upbd = i-1;
         }
      }
   }
   return(iskywd);
}