text: 
  #include <stdbool.h>
  #include <stdio.h>
  #include <string.h>
  #include <stdlib.h>
  
  // Returns 'true' if the character is a DELIMITER. bool isDelimiter(char ch)
  
   { if (ch == ' ' || ch == '+' || ch == '-' || ch == '*' ||
  
          ch == '/' || ch == ',' || ch == ';' || ch == '>' ||
  
          ch == '<' || ch == '=' || ch == '(' || ch == ')' ||
  
          ch == '[' || ch == ']' || ch == '{' || ch == '}')
  
  return (true);
  
   return (false); }
  
   // Returns 'true' if the character is an OPERATOR. bool isOperator(char ch)
  
  {
  if (ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '>' || ch == '<' ||  ch == '=')
  
  return (true);
  
  return (false);
  
  }
  
  // Returns 'true' if the string is a VALID IDENTIFIER. bool validIdentifier(char* str)
  
  
   {
  
   if (str[0] == '0' || str[0] == '1' || str[0] == '2' ||
  
  str[0] == '3' || str[0] == '4' || str[0] == '5' ||
  
  str[0] == '6' || str[0] == '7' || str[0] == '8' ||
  
  str[0] == '9' || isDelimiter(str[0]) == true)
  
  return (false);
  
  return (true);
  
  }
  Returns 'true' if the string is a KEYWORD. bool  isKeyword(char* str)
  
  
  {
  
   if (!strcmp(str, "if") || !strcmp(str, "else") ||
  
  !strcmp(str, "while") || !strcmp(str, "do") ||
  
  !strcmp(str, "break") || !strcmp(str, "continue") || !strcmp(str, "int") ||
  
  !strcmp(str, "double") || !strcmp(str, "float") ||
  
  !strcmp(str, "return") || !strcmp(str, "char") ||
  
  !strcmp(str, "case") || !strcmp(str, "char") || !strcmp(str, "size of") ||
  
  !strcmp(str, "long") || !strcmp(str, "short") || !strcmp(str, "typedef") ||
  
  !strcmp(str, "switch") || !strcmp(str, "unsigned") ||
  
  !strcmp(str, "void") || !strcmp(str, "static") ||
  
  !strcmp(str, "struct") || !strcmp(str, "goto"))
  
  return (true);
  
   return (false);
  
  } // Returns 'true' if the string is an INTEGER. bool isInteger(char* str)
  
  
  {
  
   int i, len = strlen(str);
  
  if (len == 0)
  return (false);
  for (i = 0; i < len; i++) {
  
   if (str[i] != '0' && str[i] != '1' && str[i] != '2'
  
  && str[i] != '3' && str[i] != '4' && str[i] != '5'
  
  && str[i] != '6' && str[i] != '7' && str[i] != '8' && str[i] != '9' ||
  
   (str[i] == '-' && i > 0))
  
  return (false);
  
  }
  
  return (true);
  }
  
  // Returns 'true' if the string is a REAL NUMBER. bool isRealNumber(char* str)
  
  
  
   { int i, len = strlen(str);
  
  bool hasDecimal = false;
  if (len == 0)
   return (false);
   for (i = 0; i < len; i++) {
  if (str[i] != '0' && str[i] != '1' && str[i] != '2'
  && str[i] != '3' && str[i] != '4' && str[i] != '5'
  && str[i] != '6' && str[i] != '7' && str[i] != '8' && str[i] != '9' &&
  str[i] != '.' ||
  (str[i] == '-' && i > 0))
   return (false);
  if (str[i] == '.') hasDecimal = true;
  } return (hasDecimal);
   }
  
  // Extracts the SUBSTRING. char* subString(char* str, int left, int right)
  
  
  {
  
   int i;
  char* subStr = (char*) malloc( sizeof(char) * (right - left + 2));
  for (i = left; i <= right; i++)
   subStr[i - left] = str[i]; subStr[right - left + 1] = '\0';
   return (subStr);
   }
   // Parsing the input STRING. void parse(char* str)
  
  {
  int left = 0, right = 0;
   int len = strlen(str);
   while (right <= len && left <= right) {
   if (isDelimiter(str[right]) == false) right++;
   if (isDelimiter(str[right]) == true && left == right) {
   if (isOperator(str[right]) == true)
  printf("'%c' IS AN OPERATOR\n", str[right]);
  right++;
   left = right;
  
  
  
  
  }
   else if (isDelimiter(str[right]) == true && left != right || (right == len && left != right))
   { char* subStr = subString(str, left, right - 1);
  
  if (isKeyword(subStr) == true)
  
   printf("'%s' IS A KEYWORD\n", subStr);
  
  else if (isInteger(subStr) == true)
  
   printf("'%s' IS AN INTEGER\n", subStr);
  
  else if (isRealNumber(subStr) == true)
  
  printf("'%s' IS A REAL NUMBER\n", subStr);
  
   else if (validIdentifier(subStr) == true && isDelimiter(str[right - 1]) == false)
  
  printf("'%s' IS A VALID IDENTIFIER\n", subStr);
  
  else if (validIdentifier(subStr) == false && isDelimiter(str[right - 1]) == false)
  
  printf("'%s' IS NOT A VALID IDENTIFIER\n", subStr); left = right;}}
  
  
  return;
  
   }
   // DRIVER FUNCTION int main()
  
  {
   // maximum length of string is 100 here char str[100] = "int a = b + 1c; ";
  
  parse(str);
  
  // calling the parse function
  
  return (0);
  
  }
  
  
  
  
  
  
  
  
  
  
  
  