Computer Science Canada

Number Conversion help
Author:  Klick [ Thu May 18, 2006 5:57 pm ]
Post subject:  Number Conversion help
As a part of my ecryption program for class, I would 5 numbers to be put into 1 large number, by the following sequence:

8,24,7,0,3

Large Number = 8 * (27**4) + 24 * (27**3) + 7 * (27**2) + 0 * (27**1) + 3 * (27 **0)

The number in this case would be 4729026.
Converting the 5 numbers into 1 number was fairly simple to figure out on my own. I need help recovering numbers from that large number.

I figure that i can do this using mod by the series of powers of 27, and then subtract the remainder from the total

Like so:

code:
var largenum : int
var smallnums : array 1 .. 5 of int
var power :int := 1

largenum := 8 * (27 ** 4) + 24 * (27 ** 3) + 7 * (27 ** 2) + 0 * (27 ** 1) + 3 * (27 ** 0)

for decreasing i : 5 .. 1
    smallnums (i) := largenum
    smallnums (i) := smallnums (i) mod 27 ** power
    largenum -= smallnums (i)
    power += 1
end for

for i : 1 .. 5
    put smallnums (i), "," ..
end for


It works for the last 2 numbers for some, reason, but fails miserably on the first 3.

The problem I think, is the way I am approching the solution, or I am missing something important. Any suggestions or help will be greatly appreciated.

Much Thanks!
Author:  TheOneTrueGod [ Thu May 18, 2006 6:27 pm ]
Post subject: 
code:

for decreasing i : 4 .. 0
    put largenum div 27 ** i
    largenum -= (largenum div 27 ** i) * 27 ** i
end for


Yarr, sorry for doing it entirely for you, its generally against my policy to do that, but I couldn't get this one after half a second of looking at it, so I tinkered with it till I got it Razz

I will now attempt to explain where you went wrong.

code:

for decreasing i : 5 .. 1
    smallnums (i) := largenum
    smallnums (i) := smallnums (i) mod 27 ** power
    largenum -= smallnums (i)
    power += 1
end for


The above is your code. Lets pick an arbitrary letter to represent what the first number is. I like n, so lets go with that. If we divide the "largenum" by 27**4, the resulting number will be between n * 27**4 and (n+1)*27**4. Therefore, if we truncate that number, we will get what n is. Now, just subtract n * 27**4 from the large number and repeat. One other error you made in yours is "power" started at 1, when it should have started at zero (look at the largenum calculation).
Author:  Klick [ Thu May 18, 2006 6:37 pm ]
Post subject: 
You really are TheOneTrueGod!! I knew i was missing something in it, just couldn't figure it out. Thanks a bunch. This will really help me out alot.

Thanks again!

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