'''API Calculus''' is a program that solves calculus problems using operating systems within a device that solves calculus problems. In 1989, the PI- Calculus was created by [[Robin Milner]] and was very successful throughout the years. The PI Calculus is an extension of the [http://theory.stanford.edu/~rvg/process.html process algebra CCS], a tool that haswith algebraic languages that are specific to processing and formulating statements.<ref>{{Cite web|title = Process Algebra|url = http://theory.stanford.edu/~rvg/process.html|website = theory.stanford.edu|access-date = 2015-11-09}}</ref> The PI Calculus provides a formal theory for modeling systems and reasoning about their behaviors.<ref name=":4">{{Cite book|title = An Extension to Pi-Calculus for Performance Evaluation|last = Rahimi|first = Shahram|publisher = Scientific Research|year = 2011|___location = Illinois}}</ref> In the PI Calculus there are two specific variables such as name and processes.<ref name=":4" /> But it was not until 2002 when [http://www.cs.siu.edu/research/activities/full-time/rahimi.php Shahram Rahimi] decided to create an upgraded version of the PI- Calculus and call it the API Calculus. Milner claimed the detailed characteristics of the API Calculus to be its "Communication Ability, Capacity for Cooperation, Capacity for Reasoning and Learning, Adaptive Behavior and Trustworthiness."<ref name=":3">{{Cite journal|url = http://www2.cs.siu.edu/~rahimi/papers/17.pdf|title = ACVisualizer: A Visualization Tool for Api-Calculus|last = Rahimi|first = Shahram|date = 2015-10-20|journal = ACVisualizer: A Visualization Tool for Api-Calculus}}</ref> The main purpose of creating this mobile advancement is to better network and communicate with other operators while completing a task. Unfortunately, the API Calculus is not perfect and has faced a problem with its security system. The language has seven features that was created within the device that the [[Π-calculus|PI Calculus]] does not have. Since this program is so advanced by the way the software was created and the different abilities that are offered in the program, it is required to be converted to other programming languages so it can be used on various devices and other computing languages. Although the API Calculus is currently being used by various other programming languages, modifications are still being done since the security on the API Calculus is causing problems to users.
