Lexical Analyser

/*Sample lex code for imaginary language

 *-accepts only 5 keywords namely int,float,char .
 *4-arith operators +,-,/,*
 *logical operators &-AND,!-NOT,|-OR
*/


Author : Santhosh Pai :)


#include<stdio.h>

void scan();
void iden(char);
void digit(char);
void arithop();
void logicop();
void delimiter();
int iskey(char str[]); //funtion to check a keyword
FILE *fp;

int arith=0,logic=0,del=0;

int main()
{


   fp=fopen("input.txt","r+");
   scan();
}

void scan()
{

    char ch;
    while(1)
    {
       ch=fgetc(fp);
       if((ch>=65 && ch<=90)||(ch>=97 && ch<=122))
       {
          iden(ch);
       }

       else if(ch>=48 && ch<=57)
       {
           digit(ch);
       }

      else if(ch=='*'||ch=='+'||ch=='-'||ch=='/')
       {
         arithop();
       }

       else if(ch=='&'||ch=='|'||ch=='!')
       {
         logicop();
       }

       else if(ch==' '||ch==','||ch==';')
       {
         delimiter();

       }


       else if(ch==EOF)
       break;
    }

    printf("\n The number of occurences of arithmetic operators +,*,/,-= %d ",arith);
    printf("\n The number of occurences of logical operators &,!,| = %d",logic);
    printf("\n The number of occurences of delimiter (SPACE),';' = %d",del);

}


void iden(char ch)
{
   char ident[10];

   int i=0;

   do
   {
      ident[i]=ch;
      ++i;
      ch=fgetc(fp);
   }while((ch>=65 && ch<=90)||(ch>=97 & ch<=122)||(ch>=48 & ch<=57)); //keep scanning

   //++i;
   ident[i]='\0';

   if(iskey(ident))
   {
    printf("\n %s is an keyword ",ident);
   }
   else
   {
    printf("\n %s is an identifier ",ident);
   }
   fseek(fp,-1,SEEK_CUR);//Move filepointer one step backwards


}


void digit(char ch)
{
   char dig[10];
   int i=0;
   dig[i]=ch;

   do
   {


      ch=fgetc(fp);
      if((ch>=48 && ch<=57)||ch=='.')
      {
       ++i;
       dig[i]=ch;
      }
      else if(ch=='*'||ch=='+'||ch=='-'||ch=='/')
      {
         arithop();
         break;
      }

      else if(ch=='&'||ch=='|'||ch=='!')
      {
         logicop();
         break;
      }

      else if(ch==' '||ch==','||ch==';')
      {
         delimiter();
         break;
      }




   }while(1);

   ++i;
   dig[i]='\0';

   printf(" \n %s is an number ",dig);

}

void arithop()
{
   arith++;
}


void logicop()
{
  logic++;
}
void delimiter()
{
   del++;
}

int iskey(char str[10])
{
   char ch;
   int i=0;
   while(1)
   {
      ch=str[i];
      if(ch=='i')
      {
         ++i;
         ch=str[i];
         if(ch=='n')
         {
               ++i;
               ch=str[i];

                if(ch=='t')
                 {
                       return 1;
                 }
          }

         else if(ch=='f')
         {
            return 1;
          }
       }


      else if(ch=='c')
      {
         ++i;
         ch=str[i];
         if(ch=='h')
         {
               ++i;
               ch=str[i];

                if(ch=='a')
                 {
                     ++i;
                     ch=str[i];

                       if(ch=='r')
                        {
                          return 1;
                        }
                  }
          }
        }

      else  if(ch=='f')
        {
           ++i;
           ch=str[i];
            if(ch=='l')
             {
               ++i;
               ch=str[i];

                if(ch=='o')
                 {
                       ++i;
                       ch=str[i];

			if(ch=='a')
                         {
                            ++i;
                            ch=str[i];
                             if(ch=='t')
                              {
                                 return 1;
                              }
                         }
                  }
              }
         }


         else if(ch=='e')
         {
              ++i;
              ch=str[i];
             if(ch=='l')
              {
                ++i;
                ch=str[i];

                if(ch=='s')
                 {
                     ++i;
                     ch=str[i];
                    if(ch=='e')
                      {
                        return 1;
                      }
                 }
              }


                 else if(ch=='n')
                  {
                     ++i;
                     ch=str[i];
                    if(ch=='d')
                      {
                        return 1;
                      }

                 }
           }

        else  if(ch=='b')
        {
           ++i;
           ch=str[i];
            if(ch=='e')
             {
               ++i;
               ch=str[i];

                if(ch=='g')
                 {
                       ++i;
                       ch=str[i];

			if(ch=='i')
                         {
                            ++i;
                            ch=str[i];
                             if(ch=='n')
                              {
                                 return 1;
                              }
                         }
                  }
              }
         }



         break;
     }

return 0;
}