Unknown Variable Types

[Slayer]

Alright, I'm not sure how to explain this clearly, but I'll give it a shot.

I want to make a program that will tell me the molar mass of molecules. I don't know how separate whether an integer or a variable will come next.

For instance, I give all my elements values, like
double c = 12;
couble h = 1;
double o = 16;


I don't know how to make the program know how to evaluate a person inputting H2O as well as doing OH. How can I make it take the number in the middle?

Idk, I know I'm not too clear with this and I don't have any code to show you because honestly I don't know where to start.

[pbrockway2]

You don't actually know whether a digit or a letter will come next. For a very simple case you could work along a string like "H2SO4" and test each character to see if it is a letter or a digit.

For more complex cases (integer values represented by multiple digits, lower case letters, parentheses) you are trying to tokenize and parse the string. This is fun, but may be beyond where you are now.

It might be best to describe the range of molecular expressions you are trying to work with.

[DarrylBurke]

The parser had better be case-sensitive, or sodium will break down into nitrogen and argon ;)

db

[JosAH]

The parser had better be case-sensitive, or sodium will break down into nitrogen and argon ;)

True ;-) I forgot most of those molecular expressions so here is a very simple question: do those numbers bind to the last atom or to a latest molecular sub-structure? e.g. in H2SO4 does the '4' bind to the right most 'O' or can it also bind to the group 'SO'? (I know here it binds to the single O, but it's just an example). Do parentheses occur in those expressions? If not, the parsing of such expressions is simple: {<atom><number>?}+

kind regards,

Jos

[Slayer]

You don't actually know whether a digit or a letter will come next. For a very simple case you could work along a string like "H2SO4" and test each character to see if it is a letter or a digit.

I think they are simple enough to do this. How do I test each character to tell if is a letter or a digit?

[Zack]

Get the character at a position, then invoke isDigit or isLetter.

The API is a wonderful thing!

[pbrockway2]

The Character class has a method isDigit() that is useful for this.