My Dear Aunt Sally

My Dear Aunt Sally


PEMDAS is an acronym that is taught in elementary school classrooms across the nation. It helps students remember the priority, or order of precedance, used to solve expressions involving strings of numbers and operators. It stands for:


A famaliar mneumonic that is widely used in place of PEMDAS is: Please Excuse My Dear Aunt Sally. Thus the name of this application. Kind of an inside joke for the mathematical types.

Computers, including smart phone calculators, desktops, etc. have built in functionality to properly interpret such expressions so we don't have to. But have you ever wondered what algorithms the CPU executes to get the right answer every time? This app demonstrates one such algorithm called the Shunt Yard, developed a few years back by Professor Edsger W. Dijkstra.

We’re going to take a closer look under the hood at Order of Operations algorithms. It will interest programmers and elementary students alike; for programmers, the use of queues and stacks will reinforce previous computer science learning; for students, it allows them to write an expression, then analyze it using Order of Operations rules, step by step. Its Quiz mode generates random expressions of user selected lengths and magnitudes and then grades the student's answer. Incorrect answers can be illuminated by the same step by step process.


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