# Programming Fundamentals/Program Quality
## Overview

Program quality describes basic properties of the program’s source code and executable code, including reliability, robustness, usability, portability, maintainability, efficiency, and readability.

## Discussion

Whatever the approach to development may be, the finished program should perform well in the following properties:
* Reliability: how often the results of a program are correct. This depends on the conceptual correctness of algorithms, and minimization of programming mistakes, such as mistakes in resource management (e.g., buffer overflows and race conditions) and logic errors (such as division by zero or off-by-one errors).
* Robustness: how well a program anticipates problems due to errors (not bugs). This includes situations such as incorrect, inappropriate or corrupt data, unavailability of needed resources such as memory, operating system services, network connections, user error, and unexpected power outages.
* Usability: the ergonomics of a program: the ease with which a person can use the program for its intended purpose or in some cases even unanticipated purposes. Such issues can make or break its success, regardless of other issues. This involves a wide range of textual, graphical and sometimes hardware elements that improve the clarity, intuitiveness, cohesiveness, and completeness of a program’s user interface.
* Portability: the range of computer hardware and operating system platforms on which the source code of a program can be compiled/interpreted and run. This depends on differences in the programming facilities provided by the different platforms, including hardware and operating system resources, expected behavior of the hardware and operating system, and availability of platform specific compilers (and sometimes libraries) for the language of the source code.
* Maintainability: the ease with which a program can be modified by its present or future developers in order to make improvements or customizations, fix bugs and security holes, or adapt it to new environments. Good practices during initial development make the difference in this regard. This quality may not be directly apparent to the end user but it can significantly affect the fate of a program over the long term.
* Efficiency/performance: the measure of system resources a program consumes (processor time, memory space, slow devices such as disks, network bandwidth and to some extent even user interaction): the less, the better. This also includes careful management of resources, for example cleaning up temporary files and eliminating memory leaks.
* Readability: the ease with which a human reader can comprehend the purpose, control flow, and operation of source code. It affects the aspects of quality above, including portability, usability and most importantly maintainability. Readability is important because programmers spend the majority of their time reading, trying to understand, and modifying existing source code, rather than writing new source code. Unreadable code often leads to bugs, inefficiencies, and duplicated code.
* It is crucial to note that there is no single property that is more important than the rest. The properties are best viewed as a system, each being just as important as the next. These properties support the program and if one is weak or fails, it will affect the entire program.

## Key Terms
### efficiency

    The measure of system resources a program consumes.

### maintainability

    The ease with which a program can be modified by its present or future developers.

### portability

    The range of computer hardware and operating system platforms on which the source code of a program can be compiled/interpreted and run.

### readability

    The ease with which a human reader can comprehend the purpose, control flow, and operation of source code.

### reliability

    How often the results of a program are correct.

### robustness

    How well a program anticipates problems due to errors.

### usability

    The ease with which a person can use the program.

## References

* Wikipedia: Computer programming