Anyone know a algorithm to reverse a number's order?.:Resovled:.

Hello everyone,
I'm trying to figure out how i'm suppose to ouput a number reversed, such as, 123 output it as 321.
I'm not allowed to use arrays so i'm thinking there has to be a mathamatical way of doing this. There is no fixed amount of numbers, it can be 2 to whatever the user wants to enter, any idea's? Like this almost worked....
input: 155
155%10 = 5;
15%10 = 5;
10%10 = 0;
almost got 551 :(

% is mod in C++ but u all probably knew that just making sure!
Thanks for listening:D

This is VB but...

VB Code:

Private Sub Form_Load()
Dim Inp As String
Dim i As Integer
Dim Res As String
 
Inp = InputBox("Enter a number")
Res = ""
For i = Len(Inp) To 1 Step -1
    Res = Res & Mid$(Inp, i, 1)
Next
 
MsgBox Res
End Sub

Thanks for your reply, here's what comerak showed me:

Code:

---

#include <iostream>
using namespace std;

int main()
{
    int number;
    cout << "Please enter a number (integer): ";
    cin >> number;

    while (number)
    {
        cout << number%10 << " ";
        number/=10;
    }
    cout << "\n";
    return 0;
}

---

works like a charm!

interersting example you give:

155%10 = 5
15%10 = 5
10%10 = 0

just wondering why you divided by 10 between steps one and two, but not between two and three. If you had, then i guess it would have worked.

Anyway, if you are using C++, then you may be able to save it into a string, then just either use STL to reverse it (there might be some reverse() algorithm), or just use a stack, push the digits (or characters) on, then pop off and store the new order.

If it was up to me I would have just stored each digit into an array and then started with the last element and iterate to the first element but arrays weren't allowed nor STL :rolleyes:
THanks for the advice though! :D

Quote:

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Originally posted by voidflux
Hello everyone,
I'm trying to figure out how i'm suppose to ouput a number reversed, such as, 123 output it as 321.
I'm not allowed to use arrays so i'm thinking there has to be a mathamatical way of doing this. There is no fixed amount of numbers, it can be 2 to whatever the user wants to enter, any idea's? Like this almost worked....
input: 155
155%10 = 5;
15%10 = 5;
10%10 = 0;
almost got 551 :(

% is mod in C++ but u all probably knew that just making sure!
Thanks for listening:D

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10%10 = 0 -- yep, that's true.... mod returns the remainder after division
1%10 = 1
2%10 = 2
3%10 = 3
4%10 = 4
5%10 = 5
6%10 = 6
7%10 = 7
8%10 = 8
9%10 = 9
10%10 = 0

What if you are told its a number, but its base is not fixed at ten,

ie, WIF its base is 9, 12, 16, anything? And, they use Alpha Chars for numerical representation?

I'd stick with mid if I were you.


-Lou

Hmmm, makes me wonder:

If we have some base ten number, perhaps 123456, and represent it as K in hex,
if we say that 654321 = reversed{123456},
is 654321 = Reversed{K}?

-Lou

C++ strings arent usually considered arrays, so you can use strings, and STL reverse command. or if you want mathematics,

int reverse(int n){
int t=0;
for (;n>0;n/=10) t=t*10+n%10;
return t;
}
doesnt work with negative numbers or decimals

Reversing the digits (in binary) is an important step in unscrambling the output of the Fast Fourier Transform. The only fast way I know to do it is the memory-consuming table lookup. Some compromises are possible, such as limiting the table size to 256 entries to give instant reversal of 8 bits at a time, then reversing the bytes (instead of bits) in software.

Reversing the bytes might be done by strings, as previously shown. But in your case, you are working with integers in number base ten, so you could construct while decimating:
R is the result, N is the number to be reversed.

R=0
while N>0
R:=10*R+mod(N,10)
N=N/10
wend

Only integer arithmetic is used here, and minimal memory... HOWEVER, EXTREME WARNING!!!! NOT VALID FOR NEGATIVE NUMBERS! I suspect that using the string method is equivalent to this, with the loop and logic efficiently coded by VB and invisible to you.

I apologise for any contamination by HotPaw basic. My Palm is my main machine.

One final word on the string reverse: you can use the StrReverse function instead of a loop ;)

Quote:

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Originally posted by jemidiah
One final word on the string reverse: you can use the StrReverse function instead of a loop ;)

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Not always. StrReverse was implemented in VB 6 for the first time...

From his sig.

Quote:

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Visual Studio.Net EE

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;)