Cobol tutorial for Beginners

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COBOL is a procedural language.

• Environment: Windows
• WSL: Windows Subsystem for Linux
• Linux: Debian
• IDE: VSCode (WSL extention + Cobol extensions)
• Compiler: GNUCobol

What is JCL?

JCL, Job Control Language- the scripting language for running COBOL programs

• this course won't cover this because we're not using a mainframe

Obtain input from the user

• Variables are declared in the working-storage section of the data division.
• Strings are concatenated using "," then the name of the variable.

COBOL naming standards

• Hyphen is the only special character allowed in user defined names
• WS is used to prefix variables for working storage
• DET is used to prefix variables used to write to files

How to define types of data

Variables are defined in cobol in the following way:

• level number
• data name
• picture clause
• Value (optional)

Level Numbers

• 01 Field description or group level items
• 02-49 elementary items
• 66 reserved for the rename clause
• 77 items that cannot be subdivided
• 88 condition name entities

• "HIGH-VALUES" is often used to denote the end of a file.
• "FILLER" means something that isn't used anywhere else.

Comp-3 data types

comp-3 in cobol is a "packed decimal". This compresses numbers to half their size.

This tells computers to use decimal arithmatic and not floating point.

comp-3 is declared immediately after the pic clause

Literal and figurative constants

Numeric literal can have 18 digits

• can have a decimal

figurative constants can be things like "high-values", "zeroes", etc.

Editing characters for writing reports

• Z suppresses zeroes
• , prints a comma if there is a significant figure to the left
• * is called "check protection", and it keeps a symbol between a fixed dollar sign and actual values.

Introducing to verbs

• open - opens
• initialize - sets numbers to 0 and letters to spaces
• accept - get data from computer or user
• move - moves information from one data field to another

some verbs have ending verbs: read/end-read, if/end-if

Computational verbs

Verbs that perform calculations

ADD add digits

Suppose A is 5, B is 7, C is 1

• "ADD A TO B" adds 5 to B, changing B to 12
• "ADD A TO BE GIVING C" adds 5 and 7, changing C to 12
• "ADD A B TO C" adds 5 and 7 to C, changing C to 13
• "ADD A TO B C" adds 5 to B giving 12 & adds 5 to C giving 6.

SUBTRACT performs subtraction

A 5, B 7, C 20, D 10

• "SUBTRACT A FROM B" is B-5, giving 2
• "SUBTRACT A B FROM C" is C-5-7, giving 8
• "SUBTRACT AB FROM C GIVING D" is C-5-7, storing the 8 in D

MULTIPLY

A 5, B 7, C 20

• "MULTIPLY A BY B GIVING C" 5*7 = C (35)
• "MULTIPLY A BY B" multiplies A*7, changing A to 25
• "MULTIPLY A BY 3 GIVING B C" multiplies A*5, changing B and C to 15

DIVIDE

A 5, B 7, C 20

• "DIVIDE 2 INTO C" is c/2, giving 10
• "DIVIDE 2 INTO C GIVING B" is c/2, changing B to 10
• "DIVIDE 3 INTO A GIVING B REMAINDER C" is modulo division. A/2 equals 1 R2, so B becomes 1 and C becomes 2

COMPUTE

Allows you to do math using operators

classic method

1. MULTIPLY A * A GIVING A-SQUARED
2. MULTIPLY B * B GIVING B-SQUARED
3. ADD A-SQUARED TO B-SQUARED GIVING C-SQUARED
4. COMPUTE C = (C-SQUARED)**.5

pure compute method

1. COMPUTE C = (A * A + B * B)**.5

compute statements always begin with the resulting variable set equal to the desired equation.

Conditional expressions

IF, END-IF

IF, ELSE, END-IF

Nested IF statements

can test for things:

• IS NUMERIC
• IS ALPHABETIC, IS ALPHABETIC-UPPER, IS ALPHABETIC-LOWER
• IS POSITIVE, IS NEGATIVE
• AND, OR, NOT

COMPARE

• IS GREATER THAN (>), IS LESS THAN (<)
• IS EQUAL TO (=)
• IS NOT
• IS GREATER THAN OR EQUAL TO (>=), IS LESS THAN OR EQUAL TO (<=)

EVALUATE

• EVALUATE, END-EVALUATE - basically a switch statement

Perform statement

Cobol is sequential. It starts at the beginning and executes commands until told otherwise.

The GO TO command has a limited use case, generally only for error handling, to close the files and end the program.

Perform times

"PERFORM __ UNTIL __" lets you define loops.

Challenge: Process payroll

Solution: Sample program to process payroll

Inserting records in a master data file

Updating records in a master file

Sorting records in COBOL

Merging records in COBOL

Challenge: Merge two employee files

Solution: Create a master employee file

Direct access files in COBOL

Relative files in COBOL

Indexed files in COBOL

Challenge: Create an indexed file

Solution: Solution for creating an indexed file

Using tables in COBOL

Creating tables from an input file

Searching tables in COBOL

Challenge: Create table of weather data

Solution: Search table of weather data

Inspecting strings in COBOL

Using the string command in COBOL

Using the unstring command in COBOL

Watch for numeric overflow in variables

How to read and find logic errors

Finding answers to your COBOL questions