Chapter 6 Programming Languages (2) Introduction to CS 1 st Semester, 2015 Sanghyun Park

Outline  Historical Perspective(covered)  Traditional Programming Concepts(covered)  Procedural Units  Language Implementation  Object-Oriented Programming(skip)  Programming Concurrent Activities(skip)  Declarative Programming(skip)

Procedures  A ________ is a set of instructions for performing a task that can be used as an abstract tool by other program units  ________ is transferred to the procedure at the time its services are required  Control is returned to the original program unit after the procedure ________  A procedure can be regarded as a _________ program

Flow of Control

Variables and Parameters  Local variables  Variables declared ______ a procedure  ______ to that procedure only  Global variables  Variables not ________ to a particular part of a program  Accessible __________ the program  Parameters  Variables that are passed to ____________  Formal parameters and ______ parameters

Procedures: Example

Parameter Passing  Pass by ________  There are pros and cons with each

Pass By Value  A ____ of the data represented by the actual parameters is produced and given to the procedure  Any alterations to the data made by the procedure are reflected only in the _____ --- the data in the calling program unit are ______ changed  Therefore, this model is ____  If the parameters represent large blocks of data, this can be ___________

Pass By Value: Example

Pass By Reference  The ________ of the actual parameters is given to the procedure  The procedure has ____ access of the data represented by the actual parameters  This is more ________  This is however more _________

Pass By Reference: Example

Functions  There are two types of procedures  Those that DO NOT return a value (sometimes called __________)  Those that DO return a value (usually called __________)

Language Implementation  The process of converting a program from one language to another is called _________  The program in its original form is the _______ program; the translated version is the ________ program  Translation process

Lexical Analyzer  Reads the source program symbol by symbol, ________ which groups of symbols represent single units, and _________ those units (numeric values, words, …)  As each unit is classified, the lexical analyzer generates a bit pattern known as a ______  Therefore, the lexical analyzer converts the program (a stream of _______) into a stream of _______

Parser  Identifies the ___________ structure of the program and recognizes the ____ of each component  Based on a set of syntax rules (= __________) that define the syntax of the programming language  A ______ tree is used to show that a stream of tokens conforms to the grammar

Syntax Diagram: Example 1

Syntax Diagram: Example 2

Parse Tree for x + y x z

Ambiguity  A parse tree represents the parser’s _____________ of the program’s grammatical composition  The grammar is __________ if it is possible to have more than one parse tree for one string  Note that the following statement leads to ambiguity: if B1 then if B2 then S1 else S2 (________ Else)

Parse Tree 1 for Dangling Else

Parse Tree 2 for Dangling Else

Dangling Else Resolution  _________ close every if statement, or  Match every else with the ________ if

Code Generation  Constructs the ________-language instructions to implement the statements recognized by the parser  This process involves numerous issue, one being that of producing efficient code (code __________)  Some optimizations include  Reduce number of _____instructions_____  Remove _________ and/or useless instructions  Reduce number of __jumps______

Linking and Loading  When all steps of translation have been finished, we have a piece of ______ code  Object code may contain _________ to other object code  Thus, generally several pieces of object code need to be ______ together to form an executable program  In order for an executable program to be run, it needs to be loaded into memory by a program called a ______