Scientific Notation

[whOOper]

Hi Im makin a program in c++ for chemistry conversions, but I'm having trouble with the scientific notation of a constant heres the code
#include <iostream> // This program is for basic conversions in chemistry
#include <string>

using namespace std;

int main()
{
float moles;
float atoms;
float grams;
int choice;
double const avo = 6.022e+23;

cout<<"What would you like to convert ";
cout<<"Press 1 for moles to atoms ";
cout<<"Press 2 for atoms to moles ";
cout<<"Press 3 for grams to atoms ";
cout<<"Press 4 for atoms to grams ";
cout<<"Press 5 for moles to grams ";
cout<<"Press 6 for grams to moles ";
cin>> choice;

if ( choice == 1 ) {
cout.precision(4);
cout<<"Enter a number of moles ";
atoms = moles * avo;
cin>> moles;
cout<<"The number of atoms are "<< atoms << "\n";
cin.ignore();
}
cin.get();
return 0;
}

The code I think I'm having trouble with is the stuff in bold could some one please comment. This is not for school either my school, sadly, doesn't have a programming class which sucks, but any how please help. Thanks in advanced whOOper

[Duthomhas]

The constant is Avogadro's Number, which is used to figure out how many atoms there are in a given volume of some substance.
See
http://gemini.tntech.edu/~tfurtsch/scihist/avogadro.htm
and
http://en.wikipedia.org/wiki/Avogadro%27s_number


To express 6.022 x 10²³ to a computer program, replace the "x 10" with an "e" and follow it with the exponent: 6.022e+23.

Another example: 1.6605387 x 10^-27 kg becomes 1.6605387e-27 kg.

Hope this helps.

[whOOper]

Thanks for the post, but if you look in the above code I posted with the question I did this and Im getting answers that are way off. could it possibly just be a computer error although I doubt that.

[z05DSL3A]

You are doing the calculation atoms = moles * avo; before you have a value for moles.

This will calculate 6.022e+23 multiplied by a junk value producing a junk result.

Your compiler should have given you a warning about using an initialized variable...

You may want to change you floats to doubles as well.

[whOOper]

Thanks grey wolf Im at school so i cant try the modifications, but thanks for replying

[Deimos]

Hello there,
I don't know if you're still checking up on this post but anyway I just wanted to make a little correction concerning the way you are calculating the number of atoms.

Your program is not scientificaly correct, I say this because the value you are obtaining with the operation moles * avo is the number of molecules, not atoms. In order to calculate the number of atoms you'd need to know what element we are talking about.
The oxygen molecule, O₂, for example, is composed by two atoms of oxygen. 1 mol of oxygen doesn't have 6.02e+23 atoms, it has 6.02e+23 molecules and 12.04e+23 atoms, because in this case you multiply the Avogadro constant by two.
Another example, the methane molecule, CH₄, it's 1 carbon atom and 4 Hydrogen linked together. 1 mol of methane has 6.02e+23 molecules, 6.02e+23 atoms of carbon and 4*6.02e+23 atoms of hydrogen, 26.10e+24 atoms in total (no calculator here, and i'm sleepy so I can't ensure my calculations' "rightness").

Hope this helps :)
Best Regards,
~Deimos

[whOOper]

Hi thanks for that update I just found out about that problem yesterday Im going to my chem teacher to see if he has general equations I can use. Thanks for that

[Deimos]

Glad to help!
Happy programming! :D