Log in Start free
Course

COBOL for the Mainframe

From your first DISPLAY to batch jobs that read, sort and report on real business data. Built for people training for mainframe COBOL roles.

Start lesson 1 →
01

First Steps

Where COBOL runs and why it still matters, how a program is laid out in fixed-format columns, writing output with DISPLAY, reading input with ACCEPT, and fixing the compiler errors you will inevitably hit.

8 lessons
02

Data and PICTURE

How COBOL describes data: level numbers, PICTURE strings, implied decimals and signs, VALUE and figurative constants, the rules MOVE follows, and edited pictures that turn raw numbers into report-ready text.

7 lessons
03

Arithmetic

ADD, SUBTRACT, MULTIPLY, DIVIDE and COMPUTE; rounding, overflow, numeric functions, and how COBOL stores numbers so money adds up to the cent.

8 lessons
04

Conditions

IF and EVALUATE, class and sign tests, level-88 condition names, and the period pitfalls that have caused real production outages.

8 lessons
05

Loops and Program Structure

Paragraphs, sections and every form of PERFORM, from simple calls to nested VARYING loops, and the initialise / process / terminate skeleton that nearly every batch program follows.

7 lessons
06

Tables

COBOL's arrays: OCCURS, subscripts and indexes, loading tables from input, serial and binary SEARCH, hard-coded lookup tables, two-dimensional and variable-length tables, and the out-of-range bugs that corrupt storage.

8 lessons
07

Working with Text

Slice, build, split and clean text in fixed-length fields: reference modification, STRING, UNSTRING, INSPECT and the intrinsic string functions, then parse and validate CSV data the way real interface programs do.

8 lessons
08

Sequential Files

Datasets, DD names and record layouts. Read, write, extend and update sequential files, check every FILE STATUS, and build the classic batch master-file update.

8 lessons
09

Indexed Files and SORT

Keyed access to master files (VSAM KSDS on z/OS): random reads, browsing with START and READ NEXT, adding, changing and deleting records, plus the SORT and MERGE verbs that put batch input into the order your logic needs.

8 lessons
10

Batch Reports

The printed report, still the most common output of a batch job: print line layouts, edited money, page headings and page breaks, and single- and multi-level control breaks with subtotals and grand totals.

7 lessons
11

Subprograms and Copybooks

How real mainframe systems are split into many programs: CALL with USING, the LINKAGE SECTION, BY REFERENCE and BY CONTENT, RETURN-CODE, GOBACK versus STOP RUN, static and dynamic calls, CANCEL, nested programs, and COPY copybooks that keep record layouts identical across every program that uses them.

8 lessons
12

JCL and Batch Jobs

How a batch job flows through JES, writing JOB, EXEC and DD statements, dataset dispositions, temporary datasets, SYSIN and PARM, return codes and COND, the everyday utilities IEFBR14, IEBGENER and DFSORT, and reading a job log when a step abends.

9 lessons
13

Mainframe Internals and Capstone

What your data looks like at the byte level on z/OS: EBCDIC, zoned and packed decimal, binary and SYNC. Why S0C7 happens and how to prevent it, VSAM and IDCAMS, a tour of CICS and Db2, reading abend codes and dumps, then a full end-of-day batch capstone and a plan for getting hired.

10 lessons