Modular Programming

Modular programming is an approach to software development in which the individual functions of a program are separated into self-contained components called modules. Each module contains everything necessary to fulfill its own functionality, and can be edited and modified without the entire project being affected. Modular programming is accomplished by maintaining a consistent module interface that other software components use to access each module's functions.

Modules in modular programming enforce logical boundaries between components and improve maintainability. They are incorporated through interfaces. They are designed in such a way as to minimize dependencies between different modules. Teams can develop modules separately and do not require knowledge of all modules in the system. Each and every modular application has a version number associated with it. This provides developers flexibility in module maintenance. If any changes have to be applied to a module, only the affected subroutines have to be changed. This makes the program easier to read and understand. Modular programming has a main module and many auxiliary modules. The main module is compiled as an executable (EXE), which calls the auxiliary module functions. Auxiliary modules exist as separate executable files, which load when the main EXE runs. Each module has a unique name assigned in the PROGRAM statement. Function names across modules should be unique for easy access if functions used by the main module must be exported.Languages that support the module concept are IBM Assembler, COBOL, RPG, FORTRAN, Morpho, Zonnon and Erlang, among others.

Modular programming, in the form of subsystems (particularly for I/O) and software libraries, dates to early software systems, where it was used for code reuse. Modular programming per se, with a goal of modularity, developed in the late 1960s and 1970s, as a larger-scale analog of the concept of structured programming (1960s). The term "modular programming" dates at least to the National Symposium on Modular Programming, organized at the Information and Systems Institute in July 1968 by Larry Constantine; other key concepts were information hiding (1972) and separation of concerns (SoC, 1974).

Benefits of Modular Programming

• Efficient Program Development: Programs can be developed more quickly with the modular approach since small subprograms are easier to understand, design, and test than large programs. With the module inputs and outputs defined, the programmer can supply the needed input and verify the correctness of the module by examining the output. The separate modules are then linked and located by the linker into an absolute executable single program module. Finally, the complete module is tested.
• Multiple Use of Subprograms: Code written for one program is often useful in others. Modular programming allows these sections to be saved for future use. Because the code is relocatable, saved modules can be linked to any program which fulfills their input and output requirements. With monolithic programming, such sections of code are buried inside the program and are not so available for use by other programs.
• Ease of Debugging and Modifying: Modular programs are generally easier to debug than monolithic programs. Because of the well defined module interfaces of the program, problems can be isolated to specific modules. Once the faulty module has been identified, fixing the problem is considerably simpler. When a program must be modified, modular programming simplifies the job. You can link new or debugged modules to an existing program with the confidence that the rest of the program will not change.

Further Reading

• Modular Programming and Modules Python
• Users Guide to Modular Programming Sun Microsystems
• What does Modular Programming Mean The Autopedia