compiler engineering lab#3

L A B # 3 : T R A N S L AT I O N F O R S I M P L E E X P R E S S I O N

COMPILER ENGINEERING

University of DammamGirls’ College of ScienceDepartment of Computer Science Compiler Engineering Lab

Department of Computer Science - Compiler Engineering Lab

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TRANSLATION FOR SIMPLE EXPRESSION

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FIRST..,DISCOVER MISTAKES

USING THE LEXICAL ANALYZER

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•Example(s):• When the lexeme > BSIZE• When the lexeme doesn’t match any regular definition

•Dealing with Errors:• Unget character when the lexeme• Print Error Message and exit(0)

ERROR DISCOVERY

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A SYNTAX-DIRECTED TRANSLATOR

•We shall construct a compiler that translates infix expression into postfix form.

•A notation in which the operators appear after there operands

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9 – 5 + 2 This will be translated from infix to postfix form as:

9 5 – 2 +


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ABSTRACT SYNTAX TREE FOR 9-5+2

9

-

5

+

2

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• Now, we construct a syntax-directed translator that translates arithmetic expressions into postfix form.

• To keep the initial program manageably small, we start off with expressions consisting of digits separated by ( + , - ) signs .


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design C program to translate an infix expression into postfix form

Write the program inside the main function starting with reading one character then call the functions you need .


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• Read a character from the user call it lookahead .

• Declare lookahead as a global variable to be used by all functions you need.


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• You will need three functions each will perform certain operations for the translation .

• All these function will be void (no return)• No variables will be passed through these

function• Only the global variable lookahead


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ERROR ( )

• Use this function for syntax errors • It will print this sentence :

( SYNTAX ERROR ! )

when errors appears on program.

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TERM ( )

• Check if lookahead character is a digit• If it is a digit put the character on the

screen and read another character.• If lookahead is not digit it will be a syntax

error .

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EXPR ( )• Use Expr function to check for operators..• Before start checking operators inside

expr( ) check if that character is digit use term ( ) function

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BACK TO EXPR( ) FUNCTION

• After reading one character after digit check if that character is +

• If true : read another character and check if that is digit, using term ( ) function that will perform previous steps of putting digit character on screen and read another , put ( + ) on screen

• If the character is not (+) : check if it is (-) , do the same as previous.

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• Find way to let program to handle sequence of operations using while statement .

• If the operator was not matched ( + , - ) call error() then break.


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QUESTIONS?

Thank you for listening

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compiler engineering lab#3

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