by Mark van Cuijk (2 Submissions)
Category: Math/Dates
Compatability: Visual Basic 5.0
Difficulty: Intermediate
Date Added: Wed 3rd February 2021
Rating: 
(5 Votes)
This module can be used to parse a mathematical expression given as a string. The result is just a double value, which can be used for anything you'd like to.
Inputs
A string containing an expression. Spaces between operators and operands are ignored. The following operators are supported:
- exponentiations (^)
- multiplications (*)
- divisions (/)
- modulus (%)
- additions (+)
- substractions (-)
Besides it's possible to use some built-in functions, putting parameters between braces:
- sin, asin, cos, acos, tan, atan
- int (returns integer part)
- frac (returns decimal part)
- log (logarithm with base 10)
- ln (natural logarithm with base e)
- abs (absolute value)
- sign (returns -1, 0 or 1)
- rnd (random number between 0 and param)
- sqrt (square root)
You can define your own functions. These functions are implemented in BasicFunctions.
I haven't implemented variable support, because the best way to do so depends on how you're going to use this code. The ReadVariable-function is called when the value of a variable is needed. It's your own job to implement it.
Last but not least sub-expressions are supported by encapsulating them with braces.
Example (showing some features):
12 * (14-36 ^ (-sin(-4*sqrt(18)))) / (15 * rnd(4) +1)
Assumes
Just call ParseExpression("1+1") to see what happens.
Variable support isn't implemented.
Code Returns
A double value containing the result.
Side Effects
Operator precedence:
1. Functions and variables
2. Sub-expressions
3. Exponentiations (^)
4. Multiplications (*) and divisions (/)
5. Modulus (%)
6. Additions (+) and substractions (-)
Download Expression parser (4 KB)
VBcoders