A More Useful Program
Suppose we want to calculate the resonant frequency of
an L-C circuit using the equations:
&omega L = 1 / &omega C
&omega = 2 π f
(If the Greek and maths symbols are not displaying correctly in
your browser you may wish to take this opportunity to install current Mozilla
which will do so.)
These can be rearranged to:
&omega = √(1/LC)
f = &omega / 2 π
The last two equations are now suitable formulas for
L = ...
C = ...
omega = 1/Math.sqrt (L*C)
f = omega / (2*Math.PI)
L, C, omega are variables in the program.
are going to use before you use them. There is a special instruction for this.
Here we would say:
var L, C, omega
We can choose essentially any names we like so long as they'
begin with a letter.
Note the dot and the capital M!
Upper and lower case letters
are not the same, so if I have used L I cannot subsequently
get lazy and type l.
L and C
I must be careful with the units in my equations. The best way
to avoid making mistakes is always to use the fundamental units in
equations, unless you are copying a formula which has been
specifically modified to use something else. Here this means
Henries, Farads and Hertz - not the most convienient for use, but
not to worry.
A Bit More
Let's add unit conversion to the program and build in a couple
of values to test.
We want to use inductance in microhenries which means divide by one
million to get Henries, and capacitance in picoFarads, which means
dividing by a million times a million to ger Farads. Then
I'd like my answer in MegaHertz, which means dividing Hertz by a
var omega, f, L, C
var million = 1000000
L = 12 // microH
C = 10 // pF
L = L / million // Henries
C = C / million / million // Farads
omega = 1 / Math.sqrt(L*C) // rads/s
f = omega / (2*Math.PI) // Hz
f = f / million // MHz
Everything on a line following // is ignored.
Use this facility liberally to make your programs easier to follow.
Since I am using the value 1,000,000 several times I have
defined it as a variable. this minimises the risk of typing
the wrong number of zeros. Notice that I can combine the the
var definition of a variable with setting its value.
By performing a bit of algebra I might have saved the computer the
trouble of one or two of those divisions by a million.
Don't even think about it. The computer's time is less valuable than yours. You'd probably get it wrong anyway.
The Final Program
Click here to run it.
Do view - Source to look at it.
The only things that have been added are output instructions:
When you display anything that has units, always also say
what these are!
- to provide a title for the calculation,
- to repeat the data so that the output is self contained, and
- (obviously) to show the result of the calculation.
- The instruction writeln which is like write
except that it puts a new line after whatever has been displayed.
- Both output instructions can have multiple items, separated by
commas, in the brackets after the keyword. If these are text in quotes
this is displayed exactly as specified. If they are names of variables
their vaules are displayed.
- The text<pre> at the beginning of the first output instruction.
Don't worry about why it's there meantime, just always put it in. You
might like to try removing it to see what happens..
Still more here...