Variables

[T Väntänen]

Richard Blackwood wrote:
> To All:
> 
>    Folks, I need your help. I have a friend who claims that if I write:
> 
> foo = 5
> 
> then foo is NOT a variable, necessarily. If you guys can define for me 
> what a variable is and what qualifications you have to back you, I can 
> pass this along to, hopefully, convince him that foo is indeed a variable.
> 
> Thanks all!
> 
> Richard B.

For example in physics formula for falling object distance:
d = (1/2)*g*t^2

In physics (math) d and t are variables and g is a constant. When you 
start to calculate the distance you assign some values to the variables, 
you  cant touch the constant - thats the meaning of something being 
constant. Or is g constant or variable?

Math:
For example if we want to visualize the speed of the object from 0 to 10 
seconds we need to calculate some values to d/t graph. You do this:
t = 0, calculate d
t = 1, calculate d
...
t = 10, ...

In math you maybe call that t and d are constants, but those are 
constants only for one calculation.

Programming:
In python we'd do:
---
g = 9.81
for t in range(0, 11):
     d = 0.5 * 9.81 * t
     print 't=%s d=%s' %(t, d)
---
it prints out:
0: 0.0
1: 4.905
2: 9.81
3: 14.715
4: 19.62
5: 24.525
6: 29.43
7: 34.335
8: 39.24
9: 44.145
10: 49.05

Constant is "variable which value is same through the program 
execution", variable value can change. Knowing value of variable doesn't 
make it constant.

Vocabulary and notation varies. Electric engineers might talk about 
generator, in candyshop there are surely lots of wrappers, and both 
soldiers and surgeons plan and execute operations.

HTH