Changes to the code

The use of isspace() function from ctype.h instead of checking for space and newline characters separately.
The use of a while loop instead of a do-while loop when scanning identifier names to avoid writing to the array out-of-bounds if the identifier name exceeds the maximum length.
The use of isdigit() function from ctype.h instead of checking if a character is a digit by comparing it to characters '0' to '9'.
The use of a switch statement to handle the different cases of characters that can be encountered in the input.
The lookahead() function has been simplified by returning the value returned by the lex() function directly.

added license file which was deleted accidently.