Compiler design by gate smashers

How to design a compiler?
A parser is a program that is part of the compiler, and parsing is part of the compiling process.
Parsing happens during the analysis stage of compilation.
In parsing, code is taken from the preprocessor, broken into smaller pieces and analyzed so other software can understand it..
What is a parser in compiler design?
If you really want to understand compiler construction, you will learn that it is not easy..
Rules to find First()
If X is a terminal, then First(X) is {X}.
If X is a non-terminal and X tends to aα is production, then add 'a' to the first of X. if X-\x26gt;ε, then add null to the First(X).
If X_\x26gt;YZ then if First(Y)=ε, then First(X) = { First(Y)-ε} U First(Z).
Why is first and follow important? first and follow are important because they help the parser determine which production rule to apply to the given input.
First tells which terminal can start production whereas the follows tells the parser what terminal can follow a non-terminal.

How to design a compiler?