sardarnajam

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Lab lec 01 FLex

• Ahsan Khan

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Compilation process
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Lex

• Lex is a program that generates lexical analyzer.
• The lexical analyzer is a program that transforms
  an input stream into a sequence of tokens
• It reads the input stream and produces the source
  code as output through implementing the lexical
  analyzer in the C program.

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How Lex Tool Work

• Firstly lexical analyzer creates a program lex.1
  in the Lex language. Then Lex compiler runs the
  lex.1 program and produces a C program lex.yy.c.
• Finally C compiler runs the lex.yy.c program and
  produces an object program a.out.
• a.out is lexical analyzer that transforms an
  input stream into a sequence of tokens.

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Lex file format

• A Lex program is separated into three sections by
  delimiters. The formal of Lex source is as
  follows
• Definitions include declarations of constant,
  variable and regular definitions.
• Rules define the statement of form p1 action1
  p2 action2....pn action.

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(No Transcript)
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Identifying pattern in lex
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Sample Program

• includeltstdio.hgt
• int uppercase0
• int lowercase0
• A-Z printf("Uper case letter\t")uppercase
• a-z printf("lowercasee letter\t")lowercase
  
• int main()
• printf("please enter string\n")
• yylex()
• printf("upercased and lower case
  d",uppercase,lowercase)

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Today Task

• PROGRAM LOGIC
• Write a java or c/c program that take stream
  input and identify the characters , digits and
  symbols along with number count and also identify
  the uppercase and lower case letters
• For example I will input the following text HI!
  I am john , I am 25 years old , lives in Street
  02 Holland
• Output
• Symboll
• Capital AlphabetH
• Capital AlphabetI
• Symboll !