1 Chapter 1 An Introduction to Structured Program Design in COBOL

2 Computer Program A set of instructions that enables computer to process data Also called software Two types of computer programs –Operating system programs - control overall operations of computer –Applications programs - perform tasks required by users

3 Applications Programs Written by applications programmer May provide quick solution to one-time problem –Displaying average grade for set of exam scores Or may be run on regularly scheduled basis –Program to print student transcripts each semester

4 Program Languages Machine language Only language computer understands All programs executed on computer must be in machine language Machine language programs are difficult to write

5 Program Languages Symbolic language (like COBOL) English-like languages used to write programs Easier than writing programs in machine language Must be translated or compiled into machine language to run on computer

6 Nature of COBOL Business-oriented language Standard language English-like language Relatively easy to understand

7 Standard Versions of COBOL 1960s  wide variations in COBOL compilers  first COBOL standard set by American National Standards Institute (ANSI)  second ANSI standard to make COBOL more efficient, standardized  this ANSI standard incorporated structured programming techniques

8 Program Development Process 1.Determine Program Specifications 2.Design Program Using Program Planning Tools 3.Code and Enter Program 4.Compile Program 5.Test Program 6.Document Program

9 1. Program Specifications Systems analysts, users and programmers develop specifications Specifications include: Description of input and output data Step-by-step processing required to convert input to output

10 2. Design the Program Program planning tools used to map out structure and logic of program Flowcharts use block diagrams to represent logic Pseudocode uses English-like statements Hierarchy charts (a.k.a. structure charts) show relationships among sections of program

11 3. Code and Enter Program Programmer writes and enters program into computer Program written in symbolic language (like COBOL) Called source program

12 Source program in symbolic language Object program in machine language Translated by compiler 4. Compile Source Program Compiler is program that Checks source program for rule violations Translates source program into object program

13 5. Test Program Test or debug program to ensure it contains no errors Check for two types of errors –Compile-Time Errors –Execution Errors

14 6. Document the Program Documentation - formal set of procedures and instructions to specify how to use program Written for –Those working with output –Computer operators who run program –Maintenance programmers who make modifications to program

15 Improving Program Design Two techniques used to develop programs that are easier to understand, test, debug and modify Structured Programming Top-Down Programming

16 Structured Programming Eliminates use of GO TO statements –Allowed skipping to different sections of program without returning to starting point Program logic easier to follow with "GO- TO-less" programming

17 Structured Programming Program divided into paragraphs Main paragraph or module controls logic flow using PERFORM statements Main module "performs" other modules when instructions in that module required Each module can be written and tested independently of others

18 Top-Down Programming Another technique to make programs easier to understand, test, debug and modify Develop program like term paper –Develop outline first –Add details for each of main steps –Add further refinement for more complex steps

19 Top-Down Programming For COBOL program Code main modules or routines first Code intermediate modules next Details deferred to minor modules and coded last

20 Interactive vs. Batch Programs Cobol suited for developing both types of programs Interactive programs Accept input data from keyboard Input data processed immediately Output (results) displayed on screen immediately

21 Interactive vs Batch Programs Batch programs Process large volumes of input at periodic intervals Input data read in from files Output written to files

22 Creating a Report An Input File –Fixed record layout –Data are all “jammed” together –Records are read into the computer’s memory An Output Report –Report layout –Data are spread out for easy reading –“Hardcopy” report is sent to the printer

23 The Input File There are no column headings in the input file. There are no field definitions. The data is “all crammed together” in the file. Your COBOL program must know where on field ends and the next field begins.

24 Acton Jocelyn 223 Connecticut StSan FranciscoCA Anderson Hazel 1247 Main Street Woodside CA Baker Donald 1532 Bancroft RoadBerkeley CA BroadhurstRyan J Route 3 Big Trees CA Campbell J. H Powell StreetEmeryville CA Sample Data File Notice, each row (or record) consists of 64 consecutive bytes. A record is READ into computer memory, for use in your COBOL program.

25 Input File Layout Field Length Data Class Last Name 10 Alphanumeric First Name 8 Alphanumeric Street Address 18 Alphanumeric City 13 Alphanumeric State 2 Alphanumeric Zip 5 Alphanumeric Target Contribution 4 Numeric Actual Contribution 4 Numeric Total Record 64

26 The Output Report How many spaces should there be between columns in a report? Do these spaces appear automatically? No, your COBOL program must define the exact report layout, line by line. Consider the following report layout:

27 Sample Report Layout Acton, Jocelyn 223 Connecticut St San Francisco CA Anderson, Hazel 1247 Main Street Woodside CA Baker, Donald 1532 Bancroft Road Berkeley CA Broadhurst, Ryan J Route 3 Big Trees CA Campbell, J. H Powell Street Emeryville CA 94608

28 A COBOL Program Sample Program (p. 23) Coding Form Typically, your COBOL code will be typed in ALL UPPERCASE LETTERS. Periods are very important to all COBOL programs. You will find many errors that are a result of missing periods.

29 Four Divisions of a COBOL Program IDENTIFICATION DIVISION. PROGRAM-ID. PROG1. ENVIRONMENT DIVISION. define the files used by the program DATA DIVISION. define all the variables PROCEDURE DIVISION. the logic of the program

30 IDENTIFICATION DIVISION. Two required entries –The Division Header –The PROGRAM-ID. Notice the use of periods in this division. These periods are required. Omitting or misplacing periods usually causes problems.

31 ENVIRONMENT DIVISION. This is the link between your COBOL program and the actual computer system on which it is running. All COBOL programs (in this class) will have an INPUT-OUTPUT SECTION. This section contains the FILE-CONTROL paragraph.

32 DATA DIVISION. This division will typically have two sections: –FILE SECTION. –WORKING-STORAGE SECTION. Each file listed in the ENVIRONMENT DIVISION must also be defined in the FILE SECTION of the DATA DIVISION. FD – File Description

33 PROCEDURE DIVISION Set of instructions to be executed by program Organization of instructions planned before coding begins Describes program logic and order in which instructions will be executed

34 Read/Move/Print Sequence Data is READ into computer memory Memory defines the fields of the input file Data is MOVEd to computer memory bytes that define the output report layout The report line is written to the output device (i.e., the screen, the printer or a file).