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#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
bool isValidDelimiter(char ch) {
   if (ch == ' ' || ch == '+' || ch == '-' || ch == '*' ||
   ch == '/' || ch == ',' || ch == ';' || ch == '>' ||
   ch == '<' || ch == '=' || ch == '(' || ch == ')' ||
   ch == '[' || ch == ']' || ch == '{' || ch == '}')
   return (true);
   return (false);
}
bool isValidOperator(char ch){
   if (ch == '+' || ch == '-' || ch == '*' ||
   ch == '/' || ch == '>' || ch == '<' ||
   ch == '=')
   return (true);
   return (false);
}
// Returns 'true' if the string is a VALID IDENTIFIER.
bool isvalidIdentifier(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' || isValidDelimiter(str[0]) == true)
   return (false);
   return (true);
}
bool isValidKeyword(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, "sizeof") || !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);
}
bool isValidInteger(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);
}
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);
}
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);
}
void detectTokens(char* str) {
   int left = 0, right = 0;
   int length = strlen(str);
   while (right <= length && left <= right) {
      if (isValidDelimiter(str[right]) == false)
      right++;
      if (isValidDelimiter(str[right]) == true && left == right) {
         if (isValidOperator(str[right]) == true)
         printf("Valid operator : '%c'\n", str[right]);
         right++;
         left = right;
      } else if (isValidDelimiter(str[right]) == true && left != right || (right == length && left != right)) {
         char* subStr = subString(str, left, right - 1);
         if (isValidKeyword(subStr) == true)
         printf("Valid keyword : '%s'\n", subStr);
         else if (isValidInteger(subStr) == true)
         printf("Valid Integer : '%s'\n", subStr);
         else if (isRealNumber(subStr) == true)
         printf("Real Number : '%s'\n", subStr);
         else if (isvalidIdentifier(subStr) == true
         && isValidDelimiter(str[right - 1]) == false)
         printf("Valid Identifier : '%s'\n", subStr);
         else if (isvalidIdentifier(subStr) == false
         && isValidDelimiter(str[right - 1]) == false)
         printf("Invalid Identifier : '%s'\n", subStr);
         left = right;
      }
   }
   return;
}
int main(){
   char str[10000] = "void main() { int a,b; a=10; b=a;printf( SUM of a&b is %d, a + b) } ";
   printf("The Program is : '%s' \n", str);
   printf("All Tokens are : \n");
   detectTokens(str);
   return (0);
}
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