FinTrust COBOL

💼 A modular COBOL banking simulation demonstrating core legacy financial system patterns.

FinTrust COBOL simulates the architecture of mainframe-era banking software using GnuCOBOL. It is structured as a multi-module COBOL application with a central menu driver that dynamically CALLs subprograms as shared objects — mirroring how real COBOL systems are organized in production mainframe environments.

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🏦 Architecture

The system follows a standard COBOL subprogram model:

• mainmenu.cbl — Main driver. Compiled as an executable. Routes user input to submodules via dynamic CALL statements.
• programs/ — Submodules compiled as .so shared objects (GnuCOBOL -m flag), loaded at runtime via COB_LIBRARY_PATH.

mainmenu (executable)
├── CALL "ACCTMGMT"   → programs/account_management.cbl
├── CALL "VIEWTRANS"  → programs/view_transactions.cbl
├── CALL "LEDGERSM"   → programs/ledger_summary.cbl
└── CALL "AUTHUSER"   → programs/authenticate_user.cbl

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💡 Modules

Module	Program-ID	Description
Account Management	ACCTMGMT	View, open, close, and update account records
View Transactions	VIEWTRANS	Browse transactions by account, type, or date
Ledger Summary	LEDGERSM	Summarize balances using fixed-decimal arithmetic
Authenticate User	AUTHUSER	Credential lookup via table search

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🧰 Requirements

• GnuCOBOL 3.x (sudo apt install gnucobol on Ubuntu/WSL)
• GNU Make (optional, for the Makefile build)
• Linux or WSL (Windows Subsystem for Linux)

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🔧 Build & Run

Using Make (recommended):

make        # compile all modules and main executable
make run    # launch FinTrust COBOL
make clean  # remove compiled artifacts

Manual compilation:

cobc -m -o ACCTMGMT  programs/account_management.cbl
cobc -m -o VIEWTRANS programs/view_transactions.cbl
cobc -m -o LEDGERSM  programs/ledger_summary.cbl
cobc -m -o AUTHUSER  programs/authenticate_user.cbl
cobc -x -o fintrust  mainmenu.cbl

COB_LIBRARY_PATH=. ./fintrust

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🗂 Data Division Patterns Used

• PIC 9 / PIC X — numeric and alphanumeric field definitions
• PIC 9(9)V99 — fixed-decimal for monetary values
• PIC S9(9)V99 - signed variable that can hold both positive and negative values
• OCCURS — table definitions for multi-record structures
• REDEFINES — field overlay for alternative data interpretations
• VALUE — field initialization at declaration

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📋 Review Notes

Supplementary documentation written from a code reviewer's perspective, covering the patterns, pitfalls, and mainframe concepts that matter most in production COBOL environments.

Document	Contents
COBOL Antipatterns	Top 10 patterns to flag in any review — missing AT END, unsigned fields, GO TO chains, MOVE truncation, and more
Numeric Precision	Fixed-decimal arithmetic, implied decimal V, signed vs unsigned, ROUNDED, ON SIZE ERROR
File Handling	Sequential I/O patterns, OPEN/CLOSE discipline, VSAM organizations, JCL DD context
Data Division Guide	Level numbers, PIC clause reference, OCCURS, REDEFINES, 88-levels, LINKAGE SECTION
Mainframe Concepts	z/OS vs GnuCOBOL differences, VSAM, FILE STATUS codes, JCL, RACF, batch architecture, abend codes

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📖 Purpose

Built for educational and demonstrative purposes. FinTrust COBOL is not a banking institution.

© 2026 Alexis M Vasquez, Software Engineer. All rights reserved. No financial services are provided by this software.