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#include <iostream>
#include <cmath>
#include <conio.h>
using namespace std;
int main()
{
int num, n, remainder, prime, nonprime;
remainder = num % n;
for(num=2; num<=100; num++)
{
for(n=2; n<=sqrt(num); n++)
{
if(remainder==0)
break;
else
num=prime;
}
cout<<prime<<" "<<endl;
}
getche();
return 0;
}
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aihcezs144 wrote: remainder = num % n;
aihcezs144 wrote: num=prime;
I suggest you use the single-stepping capabilities of the debugger and either "watch" some variables or add some statements to print intermediate values, as there are major problems with your code.
Is this your first attempt to programming? FYI: statement order is important, and assignment statements work one way (right to left), not both ways (as in mathematical equations).
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okay, i've tried a new one but there are sompilation errors of which i could not locate. would you please take a look and tell mw where did i go wrong. thank you
#include <iostream>
#include<cmath>
#include <conio.h>
using namespace std;
int main()
{
int num, n, remainder;
remainder=num % n;
for( num = 2; num <=100 ; num++ )
{
for (n=2; n<=sqrt(n); n++)
{
if( remainder != 0 )
break;
}
if(remainder)
{
cout <<num<< " ";
}
num++;
}
getche();
return 0;
}
modified on Friday, September 4, 2009 8:20 AM
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Seems you have removed one problem.
Compile-time and often run-time errors contain file name and line number information, use it to your advantage; and tell your IDE to always show line numbers in edit windows (for Visual Studio look here[^]).
I'm not going to provide any more help, the goal of exercises like these is for you to learn how to research, analyze, and debug; and not for others to do your work.
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aihcezs144 wrote: remainder=num % n;
Note that remainder will not change if either num or n or both do, it's just set to num%n (which looks like an invitation to a division by zero) once when that statement is executed.
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Hi,
Would you give me an example of FAMILIES of functions that I could use in a Hashtable?
Notice that I need a FAMILY of functions (that means it should depend on some random constants previously defined)
It should go from {0, K} to {0, m}
Im trying
f(x) = (a*x + b) % prime % m
where prime is larger than x, a is between 1 and prime-1, and b is between 0 and prime-1
But its not good enough.. Dunno why though
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Quake2Player wrote: Would you give me an example of FAMILIES of functions that I could use in a Hashtable?
Example: SHA family[^]. This family and additional hash function implementations can be found here[^].
Also you can find some different hash function implementations here[^].
Regards,
Nuri Ismail
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Hi
I got an Access database encrypted by an application I bought years ago and I don't have that application anymore. This application encrypted everything before saving into the database and I would like to recover some data from that DB.
I am not sure but I think this algorithm needs a key and keys are saved to the database too so I got the keys. But I am not sure about the keys having a role in encryption. This algorithm produces a ciphertext which has same the same length as its cleartext.
Here are some examples:
Cleartext Encrypted Key
Harita Mühendisi KXsmaX büpxfdmYm MA%7vbxWKIAgARC71+KEn8i3M4yIa+i6Zd384GWTZ6/bT+M+mKCKEFN35meeSE1OGzcxL8ukvvSeKh9c5o2bBF7vbZ+_14
ÇONA ÇkWq MA%vPz9ClelvBm24BrRcVmsXPtD7OOie8xG73DumSdNLlSaAIhL7L5uPB+Q5+titBzXRDisXC4NnnEWoESLU2VIx845_16
I can provide more examples if needed but I don't think they will help. As far as I know if you encrypt a text with this algorithm and use the same key every letter means another letter. For example if you look at the first example H means K, i means m. If you want I can send you the database in private.
I really need you help.
Thanks.
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Only jones can help you, tell them that spider sent you.
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 I'm aware that it's complicated.
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SimpleData wrote: I'm aware that it's complicated.
I think that may be an understatement. In order to decrypt the data you will at the least need to know the algorithm that was used to encrypt it. Added to that the encryption may have been done with a key that the user has to enter (similar to entering a password). Without these elements I think you may be facing an uphill struggle.
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I don't know which encryption algorithm used to encrypt it but I thought that someone here might recognize the output and tell me which algorithm may have been used. Maybe someone could see a pattern etc.
I am sure that no password is needed while encrypting. Only this random key may have been used.
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The whole ethos of encryption is that it should be impossible to decrypt the data just by looking at the encrypted characters. What is the point of encrypting secure information if anyone can decrypt it just by looking at it?
Do you have the original program that did the encryption, or access to the people who wrote it?
SimpleData wrote: I am sure that no password is needed while encrypting. Only this random key may have been used.
I don't think that encrypting with a random key would be a good idea!
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I don't have the application encrypted it all I have is this database right now so I can't reverse engineer it. It is not a well coded application actually and I don't think that it's really secure.
I wasn't talking about just looking at the encrypted text and solving it from your mind, maybe something may catch to your eye. Like realizing something was encoded with Base64 just by looking.
Random key for each raw is included in the database.
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A few observations:
-1- Decoding an encrypted message without the key or algorithm will in general be hard enough that nobody's going to want to bother if they're not getting paid.
-2- If the encryption algorithm is decent, decoding will essentially be impossible.
-3- This particular algorithm doesn't seem very good.
-4- Cleartext characters outside the range [A-Za-z] are unchanged.
-5- There seems to be a 1:1 correlation between cleartext characters and encrypted characters. For example, in the first line, both "a"'s map to "X" and all of the "i"'s map to "m".
-6- The key appears to be base64 encoded. Running the portion between the "%" and the "_" through a base64 decoder may make clear what it represents. Probably a translation table.
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In another words it looks like a ceasar's cipher, and my guess is that the number after "_" indicates the alphabetical shift or something, and the characters between % and _ represents the "replacment alphabet" somhow. And if it is indeed a ceasar's chiper it looks lika a copy-pasta job, since its range is a-Z and skipps your countrys special characters.
modified on Tuesday, September 1, 2009 3:41 AM
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Thank you for really useful tips. If I try to decode everything between % and _ I get meaningless text. I know ceasar's cipher because I've read Digital Fortress .
This algorithm also changes numbers. I couldn't include a number example but it does. I think we've made progress, we will solve this.
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Have you by any chance tried the common Algoprithms? Blowfish, Catfish etc?
BHM
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Originally, I want to use the Markov model to realize object tracking and I have found Markov Random Field can be used for the optimizing Multiple target tracking.
However, the background of my tracking project is changing because of the movement of the camera.
So, I want to know whether mean-shift(or HMM, Markov model)can be used for target tracking at this kind of moving background.
And, if it is recommendable for me to combine Markov Random Field with mean-shift for producing a result of robust muti-target tracking.
Thank you.
modified on Friday, September 11, 2009 11:12 AM
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Greetings,
I'm trying to determine the best way to get a polygon from a set of points. The points are not in any particularly useful order (they are the endpoints of individual lines that fill the polygon in question). How can I easily take such a set of points and figure out the vertices of a polygon from them? The polygons may have gaps inside of them. Any ideas?
Thanks,
Will
PS. Sorry about the repost from the Graphics forum. I wasn't sure whether to put it here or there, but was informed that here was a better choice.
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A quick search of the codeproject site turned up this:
Convex Hull[^]
Best Wishes,
-David Delaune
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This is a really dificult... perspective...
if the shape is solid(with enclosed points) then you can use a contracting concentric circle approach.
if you have a form of wrapping region... good luck(unless there is other structure to your data that you didn't include)
I recently did something similar (the convex polygon approach to making a vooroni tesselation(delanuy triagulation)).
you can alternativly use a line crossing approach, but this is also tricky.
it is best if the points are "ordered" either inpriciple, or by allowence, and then building up the polygon vertex(pair) by vertex(pair).
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I have search almost every ware and to be honest I can't find on site that could answer my question.
Here is the situation, I have a .EXE, lets call it BOB.exe. BOB.exe has a portion of it's code when opened in a hex editor that is readable which leaves it open to be hacked. One think that it has is an IP that sometimes need to be changed by the administer. this app connects online but all this is relevant right now.
Now what I want to do is create a program with my own algorithms that can encrypt BOB.exe yet make BOB.exe executable by any user and at the same time when opened with a hex editor you can't understand anything in it because it will be encrypted.
So far from what I read i need to encrypt bit by bit of the program.
Please help, need this in ether C++ or C# or VB.Net
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By what you describe it seems your problem is having strings in your exe that can be read by opening it with an hex editor.
If that's the case, then you can encrypt your strings using any encryption algorithm you like, and implement a decoding routine in your software. Each time you use an encrypted string, you must decode it. For example (C#):
string MyEncodedString = "#@SIRJI3893N";
MyTextBox.Text = DecodeString(MyEncodedString);
There are many encryption algorithms you can use. The simplest are based on XORing and byte swapping. They are very fast and easy to implement but must contain a fair number of operations to make it less easy to understand the encryption method.
If you use .NET, you can also have a look at the System.Security.Cryptographic namespace, which provides standard encryption algorithms. These are stronger but depend on an encryption/decryption key, which must be embedded in the exe and must be obfuscated in some way (XORing and swapping again or similar).
About .NET, you can also make your life easier by simply using an obfuscator which provides string encryption, like eazfuscator[^]. It will do all the work for you.
You should also be aware that there is no way to stop a determined attacker with enough patience and time: he will reverse engineer your decoding routine and apply it to your strings. That said, if you implement it properly, it will take time and sweat to do that.
2+2=5 for very large amounts of 2
(always loved that one hehe!)
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