COBOL basics

Lessons

1. Why COBOL still, and what it is good at
   COBOL was designed so that business people could read it. That makes it wordy, and it also makes forty-year-old code comprehensible to someone who has never seen it before —…
2. The four divisions
   Every COBOL program has the same four sections in the same order. Once you know what belongs where, you can navigate any program in seconds.
3. PICTURE clauses and how data is stored
   The PIC clause says what a field holds and how big it is. The USAGE says how it is physically stored. Getting these wrong is the single largest source of COBOL run-time failures.
4. Logic, files and calling other programs
   COBOL's control flow is small: conditionals, PERFORM loops, EVALUATE for multi-way choices, and CALL to run another program. File I/O is verb-based and always tells you what…
5. Compile, link, run — and debugging S0C7
   Source becomes an executable in two stages: the compiler produces an object module, and the binder turns that into a load module in a library. Then JCL runs it. Knowing which…