Understanding the Mainline Logical Flow Through a Program (continued) Procedural program: one procedure follows another from beginning to end Mainline logic has three distinct parts: Housekeeping: steps to get ready Main loop: instructions executed for every input record End-of-job: steps taken at end of program Break the logic down into at least three modules Programming Logic and Design, Introductory, Fourth Edition

Understanding the Mainline Logical Flow Through a Program (continued) Programming Logic and Design, Introductory, Fourth Edition

Understanding the Mainline Logical Flow Through a Program (continued) Modularization of the program: Keeps the job manageable Allows multiple programmers to work simultaneously Keeps the program structured Programming Logic and Design, Introductory, Fourth Edition

Housekeeping Tasks Housekeeping tasks: include all steps that occur at the beginning of the program Declare variables Open files Perform one-time-only tasks such as printing headings Read the first input record Programming Logic and Design, Introductory, Fourth Edition

Declaring Variables Assign identifiers to memory locations Specify the name and data type Use meaningful names and follow standards Prefixes may be used to group related variables Declare a variable for each field in a data file Programming Logic and Design, Introductory, Fourth Edition

Declaring Variables (continued) Initializing (or defining) the variable: providing an initial value Some languages provide default initial values Other languages leave variables with an unknown or garbage value Variables representing data fields in files do not need to be initialized Programming Logic and Design, Introductory, Fourth Edition

Declaring Variables (continued) Can use variables for report headings Embed any required spaces Heading can be printed using these variables Programming Logic and Design, Introductory, Fourth Edition

Declaring Variables (continued) Local variables: declared within a module Global variables: declared at the beginning of the program, and used in all modules Annotation box: flowchart symbol containing notes Data Dictionary: list of variables used in a program, with their type, size, and description Programming Logic and Design, Introductory, Fourth Edition

Opening Files Specify file name and path (location) Issue a file open command If no input file is opened, input may be accepted from the standard input device (e.g., keyboard) You must open both input and output files to be used, including printer output device If no output file is opened, standard output device (e.g., monitor) may be used Programming Logic and Design, Introductory, Fourth Edition

Printing Headings Printing headings for reports usually is done at beginning of the program or possibly for each new page Programming Logic and Design, Introductory, Fourth Edition

Reading an Input Record Reading the first input record is the last housekeeping task Interactive application: Interacts with users via keyboard or mouse input Program pauses when the read command is executed until the user enters data Delimiter: a character designated as a separator between data values Prompt: an output statement that asks the user to enter specific data Programming Logic and Design, Introductory, Fourth Edition

Reading the First Input Record (continued) Interactive input: (from a keyboard) Programming Logic and Design, Introductory, Fourth Edition

Reading an Input Record Input from a data file: Programming Logic and Design, Introductory, Fourth Edition

Checking for the End of the File After reading a file For an interactive program, EOF may be determined when: User enters a predetermined sentinel value User selects a screen option using a mouse For input from a file, the input device recognizes EOF EOF may occur on the first read If there is data, each record is processed before the next read occurs Programming Logic and Design, Introductory, Fourth Edition

Checking for End of File (continued) Programming Logic and Design, Introductory, Fourth Edition

Modules, Subroutines, Procedures, Functions, or Methods Unit of code that performs one small task Called a subroutine, procedure, function, or method Modularization: breaking a large program into modules Programming Logic and Design, Introductory, Fourth Edition

Modules, Subroutines, Procedures, Functions, or Methods (continued) Advantages of modularization: Provides abstraction Allows multiple programmers to work simultaneously Allows code reuse Makes identifying structures easier Programming Logic and Design, Introductory, Fourth Edition

Modularization Provides Abstraction Focusing on important properties while ignoring non-essential details Avoids the low-level details and uses a high-level approach Makes complex tasks look simple Programming Logic and Design, Introductory, Fourth Edition

Modularization Provides Abstraction (continued) A To-Do list with abstraction: without abstraction: Programming Logic and Design, Introductory, Fourth Edition

Modularization Allows Multiple Programmers to Work on a Problem Large programming projects can be divided into modules Modules can be written by different programmers Development time is significantly reduced Programming Logic and Design, Introductory, Fourth Edition

Modularization Allows You to Reuse Your Work Reusability: the ability to use modules in a variety of applications Reliability: assurance that a module has been tested and proven to function correctly Programming Logic and Design, Introductory, Fourth Edition

Modularizing a Program Most programs contain a main module Contains the mainline logic Accesses other modules or subroutines Rules for module names used here: Must be one word Should be meaningful Are followed by a set of parentheses Programming Logic and Design, Introductory, Fourth Edition

Modularizing a Program (continued) Calling program (or calling module): one that uses another module Flowchart symbol for calling a module: a rectangle with bar across the top Flowchart for the module contains: Module name in the start symbol exit or return in the stop symbol When a module is called, logic transfers to the model When module ends, logic transfers back to the caller Programming Logic and Design, Introductory, Fourth Edition

Modularizing a Program (continued) Programming Logic and Design, Introductory, Fourth Edition

Modules Calling Other Modules Programming Logic and Design, Introductory, Fourth Edition

Understanding Documentation All supporting material that goes with a program Two major categories: for users and for programmers Usually created by system analysts and/or tech writers May be printed or electronic (Web or CD) End users: people who use computer programs Program Documentation: Internal program documentation: comments within code External program documentation: supporting paperwork written before programming begins Programming Logic and Design, Introductory, Fourth Edition

Completing the Documentation Program documentation may contain: Output design Input description Flowcharts Pseudocode Program code listing User documentation may contain Manuals Instructional material Operating instructions Programming Logic and Design, Introductory, Fourth Edition