Converting Notes to Frequencies
OK. To calculate any frequency, you need to know three things:

First: The fact, that a tone (note ?, i'm from germany...), that sounds one octave higher has a dobbeld frequency.
So, if e.g. C has a frequency of 264 Hz, C one octave higher has 264 Hz * 2 = 528 Hz...still one octave higher it is 528 Hz * 2 = 1056 Hz - and so on.
Second, you need a start frequency of one special tone to create a function that calculates all the others.

e.g. ("concert pitch") A = 440 Hz
And last but not least: in music it is said, that one octave has 12 halftones. (7 white and 5 black keys ;-)... )

Now, it is up to you, which halftone you suppose your concert pitch to be. On an normal (non-professional) piano keyboard concert pitch A would be the 58th one. which means, that there are still 4 lower octaves. (A is the 10th out of the 12, and 10 + 4*12 = 58)
...all these mathamitical and musical theorie, sorry...

Growing exponentially, the function has the following form: f(n) = k * a^n.

You know, the 58th halftone has a freq of 440.
One octave higher, the 70th halftone (58+12=70) has a dobbeled freq of 880.

good. that means:

440 = k * a^58 and

880 = k * a^70

Now you transform both equqtions to "k = ...", set them equal, and calculate a with 2^(1/12). Now you use the caclulated a in one equation to get k with 440 * 2^(-58/12).

Now, you have your equation f = 440 * 2^(-58/12) * (2^(1/12))^n which is equal to:

f = 440 * 2^((n - 58)/12)
And that's it !

I will give you some examples:


note / tone
 
n
 
frequency in Hz
...
...
...
B (one octace below)
48
246.9
C
49
261.6
C sharp (D flat)
50
277.2
D
51
293.7
D sharp (E flat)
52
311.1
E
53
329.6
F
54
349.2
F sharp (G flat)
55
370.0
G
56
392.0
G sharp (A flat)
57
415.3
A
58
440
A sharp (B flat)
59
466.2
B
60
493.9
C (next octave)
61
523.3
...
...
...

So far, so good.

Now, it is up to you, to create a code, that can play meldoies. Maybe you would like to have a function first, that converts the note-string ("c", "g", "d flat", "g sharp",...) to a frequency. Than you may need a good way of storing the melodie-data (with note length and so on); a playing engine; even a midi-driver is possible... :D

But this is not what I am going to do for you. :D