Pycalc

Pycalc is a simple expression calculator. It can evaluate mathematical expressions, and output the result of the evaluation.

How it works

1. Scan the expression
   • Check for malformed expression and invalid characters
   • Tokenize the expression (I wrote a custom parser to do this)
2. If there are any parantheses, replace the parantheses with the result of the sub-expression.
3. Evaluate the overall expression (which should no longer have any parantheses)

Rather than building a tree from the expression (which is the recommended approach), I have opted to perform the substitutions in-place. This means that the result of an operation replaces the operation itself.

The reason I chose to do this, is that my parsing algorithm considers everything inside parantheses as a single token. Therefore, it is fairly easy to replace this token with the result of the expression within the parantheses.

Features

• Order of operations
• Arbitrary whitespace
• Parantheses
• Simple error checking

To-do

• Simple algebraic parsing (assign values to variables, etc.)
• More robust error-checking