Algorithm to determine if a number A is a power of B.

[Moneo]

Ah, yes, he does say they must be whole numbers.
New program:
[syntax="QBASIC"]
cls

b% = -1
num% = -1
while (b% <= 0) or (num% <= 0)
line input "Number: ", num$
line input "Base: ", b$

num% = int(val(num$))
b% = int(val(b$))

if b% <= 0 then
print "Invalid base; must be greater than zero."
print
elseif num% <= 0 then
print "Invalid number; must be greater than zero."
print
end if
wend

' calculate the exponent.
exponent! = log(num%) / log(b%)
if exponent! <> fix(exponent!) then
print num$ + " is not an integer power of " + b$
else
print num$ + " is a power of " + b$ + " (exponent=" + ltrim$(str$(int(exponent!))) + ")"
end if
end
[/syntax]

Sample:

Code:

Number: 78125
Base: 5
78125 is a power of 5 (exponent=7)

-shiftLynx

Yes, the laws of logs make for a good solution.
However, the output of your entry does not look like the sample above. It does not say if in fact it is a power of the base number. It just displays the exponent, which could have decimals when it is NOT a power.

Also, you input the values into strings and convert them to integers. If an input has a non-numeric character, the VAL will just ignore it and proceed with whatever is left. Not very clean code.

If the A value is greater that 1 and the B value is 1, you get a error of "division by zero".

All in all, your solution needs more work.
*****

[Moneo]

Not exactly sure if this is what you want, but it seems simular to the above ones so I'll go on and submit:

Sorry, its late, give me a chance to try yours tomorrow.
*****

[Mitthrawnuruodo]

And mine?

[shiftLynx]

Yes, the laws of logs make for a good solution.
However, the output of your entry does not look like the sample above. It does not say if in fact it is a power of the base number. It just displays the exponent, which could have decimals when it is NOT a power.

Also, you input the values into strings and convert them to integers. If an input has a non-numeric character, the VAL will just ignore it and proceed with whatever is left. Not very clean code.

If the A value is greater that 1 and the B value is 1, you get a error of "division by zero".

All in all, your solution needs more work.
*****

1) Did you actually run the program? It does tell you whether the number is a power of the base number. If it isn't it tells you that it isn't a power. If it does, it tells you what the power is.

2) Algorithms can contain loops.

3) Division-by-zero, fine that is an unforeseen consequence. But very simple to fix.

4) If you expected somebody to check that the input was actually a number and not that some incompetent fool input characters as a number, why didn't you say that? It's clean code because it's not unnecessarily cluttered.

5) All in all, I think your judging is flawed and this "challenge" is a joke. It is trivial to determine whether a number is a power of a given base, as shown by my program which implements extremely simple math.

Why didn't you make the challenge: "Write an algorithm to find out which number must be added to A to make B". It would be equally trivial.

These challenges are awful.


By the way, your original challenge stated to write an algorithm, so:

1) Given A^x = B where A and B are known, positive integers (where A > 1), use x = ln(B) / ln(A) to determine a value of x.
2) If x is an integer value then B is an integer power of A.

That actually meets your original challenge requirements.

-shiftLynx

[edit: typo]

[Mitthrawnuruodo]

Oh, ya thanks...Unnecessarially Cluttered, my FOOT!

There's a way to check for an intger in 1 line, Z!re knows it, I forgot it, Z!re left, its on Pete's somewhere.

If you don't like this challege then shut up, and go on your way! :evil:

[Moneo]

Not exactly sure if this is what you want, but it seems simular to the above ones so I'll go on and submit:

[syntax="qbasic"]CLS
INPUT "Input Number: ", num1
INPUT "Input its #th root to check: ", num2
tst! = (num1) ^ (1 / num2)
text$ = STR$(tst!)
cont = 0
DO
cont = cont + 1
IF cont = LEN(text$) THEN EXIT DO
IF MID$(text$, cont, 1) = "." THEN PRINT num2; " is not the #th root of"; num1: END
LOOP
PRINT num2; " is the #th root of "; num1[/syntax]

Sorry, I don't understand your logic.
The program runs, but if I give it 8 then 2
it says 2 is not the #th root of 8,
whateever #th root means.
I tried 25 then 5, and got the same error message.

Have you tested it?
*****

[Moneo]

Oh, ya thanks...Unnecessarially Cluttered, my FOOT!

There's a way to check for an intger in 1 line, Z!re knows it, I forgot it, Z!re left, its on Pete's somewhere.

If you don't like this challege then shut up, and go on your way! :evil:

Thanks Mit, exactly my feelings.
*****

[Neo]

Ok, I made this thing during a project class at uni during a break... so don't expect me having tested it, I just wrote it from my thoughts right away

[syntax="QBASIC"]DECLARE FUNCTION GetExponent%(Value AS INTEGER, BaseValue AS INTEGER)

'/********************************************************************
' Calculates and returns the integer exponent of BaseValue^x=Value,
' if it exists, in which x is a positive integer number in I.
' Value and BaseValue are required to be postive integer numbers
' Returns -1 if the exponent doesn't exist
' The parameters and return value all span I-positive < 32767
' ********************************************************************/
FUNCTION GetExponent(Value AS INTEGER, BaseValue AS INTEGER)
' /*****************************************************
' Exclude some general mathematical exceptions to LOG
' *****************************************************/
IF BaseValue = 1 AND Value <> 1 THEN
GetExponent = -1: EXIT FUNCTION
ELSEIF (BaseValue = 1 AND Value = 1) OR (BaseValue = 0 AND Value = 0) THEN
GetExponent = 1: EXIT FUNCTION
END IF
IF BaseValue < 1 OR Value < 0 THEN
GetExponent = -1: EXIT FUNCTION
END IF

'/**********************************
' Calculate the exponent required
' **********************************/
Exponent# = LOG(CDBL(Value)) / LOG(CDBL(BaseValue))

'/**********************************************************
' See if it is an integer exponent and return it if it is
' **********************************************************/
IF Exponent# = INT(Exponent#) THEN
GetExponent = INT(Exponent#)
ELSE
GetExponent = -1
END IF
END FUNCTION
[/syntax]Forgive me this bad-looking code, I haven't coded in a while so it may look a bit messy.

You can call it like
[syntax="QBasic"]PRINT GetExponent(128, 2) 'should return 7 because 2^7=128[/syntax]

A small UI program incorporating this can be as follows (warning: simple and bad code (don't have much time to do complex fun))
[syntax="QBASIC"]INPUT "Enter the value:", v%
INPUT "Enter the base:", b%

e% = GetExponent(v%, b%)
IF e% = -1 THEN
PRINT "The integer exponent of value "; v%; " and base "; b%; " does not exist"
ELSE
PRINT "The integer exponent of value "; v%; " and base "; b%; " equals "; e%
END IF[/syntax]

Hope it works

[na_th_an]

I just wanted to point out something: Algorithms can have loops. Upon my definitions, a program is a collection of routines and subroutines, which are made of algorithms.

For example, the bubble sort is called "bubble sort algorithm" and it contains loops.

[KiZ]

There's a way to check for an intger in 1 line, Z!re knows it, I forgot it

Thats easy

Code:

IF a = INT(a) THEN 'its an integer!