## Balancing chemical equations (chemeq).

Description: The program calculates the coefficients of the reactants and products of a chemical
reaction in order to balance the equation entered by the user. Enter the (unbalanced) equation using the format:

reactant1 + reactant2 ... -> product1 + product 2 ...

Entering "H" instead, displays a short help text.

Programming notes: The program uses a brute force approach to determine the coefficients. This
may result in thousands and thousands of calculations to be done. Whereas for "normal" equations, this doesn't really matter
and the answer is more or less instantaneous, for complicated equations, containing 6 molecules and coefficients greater than
10, it may take time. Al + NH4ClO4 -> Al2O3 + AlCl3 + H2O + N2 (balanced: 10Al + 6NH4ClO4 -> 4Al2O3 + 2AlCl3 + 12H2O + 3N2)
took some 15 secs on my machine; but these "extreme cases" are very rare in practice.

Coefficients are calculated by generating all size (reactants + products) combinations (including repetitives) of the integers
from 1 to a presupposed maximum coefficient value. The program first tries with CoeffMax = 6, then CoeffMax = 12 and finally,
if the equation is still not balanced, asks the user if it should continue trying. This has been done to limit calculation
time on slower computers, considering that it's rather rare to have equations with coefficient
maxima greater than 6.

Version 1.1 (August 2018): Bug fixed: Equations with molecules containing "{Atom}10" or "({Atoms})10"
are correctly balanced now.

Improvements: Gaining lots of speed by eliminating those combinations which can't be the
searched coefficients (e.g. if 1 1 1 1 is not the solution, 2 2 2 2 and 3 3 3 3 can't be either). Another way to limit
the number of calculations would be to sort the combinations differently (2 2 3 1 is lots more probable than 1 1
1 12...)

Free Pascal features: Recursion, string extraction, complex Pascal data structures.

Screenshot: