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1 Week 2 Questions / Concerns Schedule this week: Homework1 & Lab1a due at midnight on Friday. Sherry will be in Klamath Falls on Friday Lexical Analyzer

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2 In-Class Exercise #3 Create a test program as input to Lab1b Add some preprocessor directives 1 - short program with one function. 1 – slightly longer program with at least 2 functions. Identify all the keywords of your language (your subset) Identify all the operators Identify all the symbols Identify all constants

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3 Test Program: Subset of C #define MAX 10 int globalx; int main() { int x, i; scanf(“%d”, &x); //scanf needs a format & a lvalue if (x <= MAX) { printf(“%d\n”, x); } else { globalx = x; i = x; while (i >= 0) { globalx = globalx + 1; --I; } } return 0; }

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4 List of Keywords int void char double if else while scanf printf return

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5 List of operators = += -= *= /= %= == != >= + - * / % ++ --

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6 List of symbols (){};‘“,(){};‘“,

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7 List of Constants int: 35 double: char: ‘a’ string literal: “%d\n” Identifiers:Letters & digits, must start with letter abc12x, index, i, j

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8 Lexical Analyzer Either process each line at a time or load the entire program into a buffer. Two ways to break program text into tokens: Use delimiters (whitespace, ;, (, ), =,, …… etc.) Use regular expressions or DFA Need a keyword table to check for keywords Need to produce a list of tokens Symbol table is not needed in this step. It checks for lexical errors (illegal characters/tokens) but syntax checking is not done in this step. Syntax errors in input test program are not checked in lexical analyzer.

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9 DFA for identifiers Regular Expression for identifiers ( a..zA..Z)(a..zA..Z0-9)* a..zA..Z a..zA..Z0..9

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10 Implementing DFA 1. Simulate the DFA with states and transitions

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DFA as graphs A Deterministic Finite Automate (DFA) can be viewed as a graph (abstract data structure) For example, this is a graph with 2 vertices (q0, q1) and 2 edges. In this case, the edges are directed. a q0 q1 a

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Graph representation A graph can be represented as –Adjacency list –Incidence list –Adjacency matrix –Incidence matrix In our case, we want to represent our DFA as a transition table.

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Machine 1: A machine that accepts even number of a’s. a a q0 q1 a q0 q1 q0 Final State: q0

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Machine 2: A machine that accepts integers 0..9 q0 q1 0 q0 q1 Final State: q q

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Machine 2: A machine that accepts integers 0..9 q0 q a a q0 q1 Machine 1: Even number of a’s

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Combining two machines: Correct version (trap states implied) 1..9 q0 q a a q2 q3 a

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q1 0 q0 1 q a q2 q3 q2 q3

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18 Implementing DFA 1. Simulate the DFA with states and transitions 2. Simulate the DFA with looping constructs.

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19 DFA_ID function if (isalpha(first character in input buffer)) { //check for more letters and digits while (isalnum(next character in input buffer)) //keep grabbing characters and put them in //currentToken buffer } //Check the currentToken to see if it’s a keyword and set //its type correctly. //Add it to the token list

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20 Lexical Analyzer Lexical Analyzer is just a combination of many DFAs DFA_ID DFA_number DFA_symbol DFA_operator DFA_stringliteral “ Anything but “ “

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Other misc. notes about Lab#1 The program is to be written in C++. You are welcome to use STL, Boost or other C++ libraries. Documentation is a part of the grade. Please follow the CSET coding guidelines posted on the class webpage. Please submit your data files with the lab so Sherry can test your lab.

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