What is the difference between a keyword and an identifier? Why must a scanner save the text of tokens? How does a scanner identify lexical errors? How does it respond? What is a pragma? What is the...

What is the difference between a keyword and an identifier? Why must a scanner save the text of tokens? How does a scanner identify lexical errors? How does it respond? What is a pragma? What is the inherent “big-O” complexity of parsing? What is the complexity of parsers used in real compilers?