UP Lecture 03

Compilers
Lexical Analysis
(202401)

1. jgs Compilers Lecture 03: Lexical Analysis Dr. Javier Gonzalez-Sanchez jgonzalezs@up.edu.mx
2. Dr. Javier Gonzalez-Sanchez | Compilers | 2 jgs High-Level Languages X,E,G,O,O #e1,I,I,0,7 @ OPR 19, AX STO x, AX LIT 5, AX OPR 21, AX LOD #e1,AX CAL 1, AX OPR 0, AX 5 Virtual Machine (interpreter) // sorce code int x; int foo () { read (x); print (5); } main () { foo (); } Lexer Parser Semantic Analyzer Code Generation 01001010101000010 01010100101010010 10100100000011011 11010010110101111 00010010101010010 10101001010101011 Assembler compilation execution
3. Dr. Javier Gonzalez-Sanchez | Compilers | 3 jgs Key Ideas Lexical Alphabet Symbol String (items) Word Token Rules Regular Expression Deterministic Finite Automata
4. Dr. Javier Gonzalez-Sanchez | Compilers | 4 jgs Let’s Work How many strings (words), and what is the token for each? Are there errors?
5. Dr. Javier Gonzalez-Sanchez | Compilers | 5 jgs Lexical Analysis 1. int x = 5; 2. float y = "hello; 3. String @z = "9.5"; 4. int x = cse340; 5. if ( x > 14) while (5 == 5) if (int a) a = 1; 6. x = x; for ( ; ; ); 7. y = 13.45.0; 8. int me = 99999000001111222000000111111222223443483045830948; 9. while { x != 9} (); 10. int {x} = 10;
6. Dr. Javier Gonzalez-Sanchez | Compilers | 6 jgs Line 1. int x = 5 ; String Word Keyword String Word Id String Word Operator String Word Integer String Word Delimiter Token → 5 items, all correct, 5 words
7. Dr. Javier Gonzalez-Sanchez | Compilers | 7 jgs Line 2. float y = "hello; String Word Keyword String Word Id String Word Operator String --- --- Token → 4 items, 3 correct, 3 words + 1 wrong item
8. Dr. Javier Gonzalez-Sanchez | Compilers | 8 jgs Line 3. String @z = "9.5" ; String Word Keyword String --- --- String Word Operator String Word Value (String Type) String Word Delimiter Token → 5 items, 4 correct, 4 words + 1 wrong item I decide to ignore @Tags capability of Java
9. Dr. Javier Gonzalez-Sanchez | Compilers | 9 jgs Line 4. int x = cse340 ; String Word Keyword String Word Id String Word Operator String Word Id String Word Delimiter Token → 5 items, all correct, 5 words
10. Dr. Javier Gonzalez-Sanchez | Compilers | 10 jgs Line 5. if ( x > 14 21 items, all correct, 21 words ) while ( 5 5 == ) if ( int a ) a = 1 ;
11. Dr. Javier Gonzalez-Sanchez | Compilers | 11 jgs Line 6. 10 items, all correct, 10 words x = x ; for ( ; ; ) ;
12. Dr. Javier Gonzalez-Sanchez | Compilers | 12 jgs Line 7. y = 13.45.0 ; String Word Id String Word Operator String Word Delimiter String --- --- Token → 4 items, 3 correct, 3 words + 1 wrong item
13. Dr. Javier Gonzalez-Sanchez | Compilers | 13 jgs Line 8. int me = 99999000001111222000000111111222223443483045830948 ; 5 items, all correct, 5 words
14. Dr. Javier Gonzalez-Sanchez | Compilers | 14 jgs Line 9. 9 items, all correct, 9 words while { x != 9 } ( ) ;
15. Dr. Javier Gonzalez-Sanchez | Compilers | 15 jgs Line 10. 7 items, all correct, 7 words int { x } = 10 ;
16. jgs Survey
17. Dr. Javier Gonzalez-Sanchez | Compilers | 17 jgs Lexical Analysis 1. How many items in the following line? int x = 5; float y = "hello; 9 Answer
18. Dr. Javier Gonzalez-Sanchez | Compilers | 18 jgs Lexical Analysis 2. How many items in the following line? String@z="9.5";intx=cse340;if(x> 14) 14 Answer
19. Dr. Javier Gonzalez-Sanchez | Compilers | 19 jgs Lexical Analysis 3. How many items in the following line? while() 3 Answer
20. Dr. Javier Gonzalez-Sanchez | Compilers | 20 jgs Lexical Analysis 4. How many items in the following line? (5 == 5) if (int a) a = 1; 14 Answer
21. Dr. Javier Gonzalez-Sanchez | Compilers | 21 jgs Lexical Analysis 5. How many items in the following line? x = x; for ( ; ; ); 10 Answer
22. Dr. Javier Gonzalez-Sanchez | Compilers | 22 jgs Lexical Analysis 6. How many items in the following line? y = 13.45.0; 4 Answer
23. Dr. Javier Gonzalez-Sanchez | Compilers | 23 jgs Lexical Analysis 7. How many items in the following line? int me =99999000001111222000000111111222223443483045830948; 5 Answer
24. Dr. Javier Gonzalez-Sanchez | Compilers | 24 jgs Lexical Analysis 8. How many items in the following line? while { x != 9} ();int {x} = 10; 16 Answer
25. Dr. Javier Gonzalez-Sanchez | Compilers | 25 jgs Lexical Analysis 9. How many items in the following line? "hello "world" bye" 3 Answer
26. jgs Test Yourselves
27. Dr. Javier Gonzalez-Sanchez | Compilers | 27 jgs Test Yourselves 1. void metodo ( int parametro ) { } 2. char w ; int w ; float w ; 3. hola mundo :-) 4. (5 == 5) if (int a) for 5. x = x + x < x / x ( x ) 6. float == int 7. 0xFF < > 512 8. for if int while void + 1/0 9. 5e-1-1-1-1-1-x
28. Dr. Javier Gonzalez-Sanchez | Compilers | 28 jgs Questions
29. jgs Compilers Javier Gonzalez-Sanchez, Ph.D. jgonzalezs@up.edu.mx Spring 2026 Copyright. These slides can only be used as study material for the Compilers course at Universidad Panamericana. They cannot be distributed or used for another purpose.