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Program Modularization in High-level Languages

Instructor: David Gloag
In this lesson, we will define program and program modules, and look at how program modules are invoked. We will also define a library in terms of computer programming and discuss how it relates to a program.

The Impact of Computers

In a technology-based society like ours, computers affect many aspects of our lives. They are behind the weather reports we consume, they influence the tasks we perform at work. With the near ubiquitousness of smartphones, we even carry them around in our pockets or purses. Some would go so far as to say they impact almost every aspect of our life. But if they are so far reaching, how do we control them? How do we make them do the specific things we want we want them to do? A few different methods have been tried over years, each with varying success. But the one that has proven to be successful is the concept of a program.

What is a Program?

A program is a series of statements or commands. The series is executed by a computer system to perform some meaningful task. Some programs are very small, requiring only a few statements. Others are rather large, made up of hundreds or thousands of statements. No matter the size, programs provide a computer with an essential piece of the puzzle, the instructions needed to perform the indicated task. For example, developers at Microsoft created a program called Word that provides word processing capabilities. And they're not alone. Developers at Apple, Amazon, and even Walmart are hard at work creating their own programs designed to help their employees and customers.

What is a Program Module?

A program module is a high-level language construct, typically part of a program, that groups a series of statements together that perform a related task so that they can be accessed as a single entity. A high-level language is a computer programming language where each command translates to several machine language commands. Program modules generally take one of two forms:

  • Sub-Programs - These are also known as functions, procedures, modules, subroutines, and routines. These entities can be invoked by name, without repeating the statements that make them up. This also speeds up development, reduces errors, and increases reuse.
  • Objects - These are complex entities that group together one or more sub-programs with the information those subprograms manipulate. Think of an object like a self-contained unit. They have similar advantages to subprograms.

These entities above have a couple of features worth noting. They include:

  • Local Variables - This is a labeled memory allocation that has a local scope, meaning that it is only visible within the program module in which it is defined. This is in contrast to a global variable which can be seen anywhere in a program.
  • Parameters - This is a piece of information that can be passed in or out of a sub-program or object. Passing is done by value, where a copy is made and updated by the entity, or by reference, where the address is used and the actual value can be updated.

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