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Help needed with Caesar Cipher

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Join Date: Apr 2009

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Gewalop

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Newbie Poster

Help needed with Caesar Cipher

Apr 23rd, 2009

Hi, I'm trying to write a code for Caesar Cipher, I don't seem to be able to get it right, I'm having no compiling errors, but there're some real logical errors, the encryption function is working fine, but I'm having troubles with the decryption.
I'd love it if someone helps me, but please if you can make the decryption function work the same way the encryption one works, I mean "mathematically".

thx very much in advance

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include<iostream.h>
#include<string.h>
#include<windows.h>
void CaesarEncrypt(char word[],int key,int size);
void CaesarDecrypt(char word[],int key,int size);
void GetWord(char word[],int &size);
void PrintArray(char array[],int n);
int main()
{
	int key,size=-1;
	char word[100];
	char choice;
		cout << "Enter the word please:\n";
	GetWord(word,size);
	cout << "Please enter the key\n";
	cin >>key;
		cout << "Enter \"e\" to encrypt, \"d\" to decrypt\n";
		cin>>choice;
		switch (choice)
		{
			case 'E':case 'e':CaesarEncrypt(word,key,size);break;
			case 'D':case 'd':CaesarDecrypt(word,key,size);break;
		}
	PrintArray(word,size);
	return 0;
}
 
void CaesarEncrypt(char word[],int key,int size)
{
	for (int i=0;i<size;i++)
	{
		if (word[i]>64&&word[i]<91)
		{
			word[i]=(char)(((word[i]+key-65)%26)+65);
		}
		if (word[i]<123&&word[i]>96)
		{
			word[i]=(char)(((word[i]+key-95)%26)+95);
		}
 
	}
}
 
void CaesarDecrypt(char word[],int key,int size)
{
	for (int i=0;i<size;i++)
	{
		if (word[i]>64&&word[i]<91)
		{
			word[i]=(char)(((word[i]-key-65)%26)+65);
		}
		if (word[i]<123&&word[i]>96)
		{
			word[i]=(char)(((word[i]-key-95)%26)+95);
		}
 
	}
}
 
void GetWord(char word[],int &size)
{
	do
	{
		size++;
	word[size]=cin.get();//cin.get() was added by Maya Shallouf
	}
	while (word[size]!='\n');//'\n' was added by  Maya Shallouf
}
 
void PrintArray(char array[],int n)
{
	for (int i=0;i<n;i++)
	{
		cout << array[i];
	}
	cout <<endl;
}
#include<iostream.h>
#include<string.h>
#include<windows.h>
void CaesarEncrypt(char word[],int key,int size);
void CaesarDecrypt(char word[],int key,int size);
void GetWord(char word[],int &size);
void PrintArray(char array[],int n);
int main()
{
	int key,size=-1;
	char word[100];
	char choice;
		cout << "Enter the word please:\n";
	GetWord(word,size);
	cout << "Please enter the key\n";
	cin >>key;
		cout << "Enter \"e\" to encrypt, \"d\" to decrypt\n";
		cin>>choice;
		switch (choice)
		{
			case 'E':case 'e':CaesarEncrypt(word,key,size);break;
			case 'D':case 'd':CaesarDecrypt(word,key,size);break;
		}
	PrintArray(word,size);
	return 0;
}

void CaesarEncrypt(char word[],int key,int size)
{
	for (int i=0;i<size;i++)
	{
		if (word[i]>64&&word[i]<91)
		{
			word[i]=(char)(((word[i]+key-65)%26)+65);
		}
		if (word[i]<123&&word[i]>96)
		{
			word[i]=(char)(((word[i]+key-95)%26)+95);
		}

	}
}

void CaesarDecrypt(char word[],int key,int size)
{
	for (int i=0;i<size;i++)
	{
		if (word[i]>64&&word[i]<91)
		{
			word[i]=(char)(((word[i]-key-65)%26)+65);
		}
		if (word[i]<123&&word[i]>96)
		{
			word[i]=(char)(((word[i]-key-95)%26)+95);
		}

	}
}

void GetWord(char word[],int &size)
{
	do
	{
		size++;
	word[size]=cin.get();//cin.get() was added by Maya Shallouf
	}
	while (word[size]!='\n');//'\n' was added by  Maya Shallouf
}

void PrintArray(char array[],int n)
{
	for (int i=0;i<n;i++)
	{
		cout << array[i];
	}
	cout <<endl;
}

Last edited by Gewalop; Apr 23rd, 2009 at 1:29 pm.

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Join Date: Mar 2008

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Sky Diploma Sky Diploma is offline

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Practically a Master Poster

Re: Help needed with Caesar Cipher

Apr 23rd, 2009

I think you should send the argument "word" as a reference and not copies of the argument.

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jephthah

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Posting Virtuoso

Re: Help needed with Caesar Cipher

Apr 23rd, 2009

i actually worked at a place that used a Caesar Cipher to encrypt user passwords for the operators who ran the production equipment.

and the "encrypted" password file was stored locally on every production computer.

no joke.

my first day there, i was like.... "LOL, WUT?"

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Join Date: Apr 2009

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Gewalop

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Newbie Poster

Re: Help needed with Caesar Cipher

Apr 24th, 2009

•

Originally Posted by Sky Diploma

I think you should send the argument "word" as a reference and not copies of the argument.

My friend... oh my friend
word is (as you see) an array, and the name "word" as a fixed pointer at the first item in the array ,so when you send it to the function , you do it like this.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
func(int array[])
{
}
int array[50];
func(array);
func(int array[])
{
}
int array[50];
func(array);

----------------------

People please... I need help

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Join Date: Oct 2007

Posts: 794

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siddhant3s siddhant3s is offline

Offline

Master Poster

Re: Help needed with Caesar Cipher

Apr 24th, 2009

>>I think you should send the argument "word" as a reference and not copies of the argument.
He is passing a pointer actually.

>>the encryption function is working fine, but I'm having troubles with the decryption.
Even Encryption is not good. Here is the output:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
siddhant3s@Xion:~/Documents$ ./testofcallbyreference
Enter the word please:
mathematically
Please enter the key
5
Enter "e" to encrypt, "d" to decrypt
e
rf_mjrf_nhfqqd
siddhant3s@Xion:~/Documents$ ./testofcallbyreference
Enter the word please:
mathematically
Please enter the key
5
Enter "e" to encrypt, "d" to decrypt
e
rf_mjrf_nhfqqd

So, what is the error?
I think you may have guessed.
Check if the Resultant character exceeds 'z' or 'Z' , If it does do the needfull

Siddhant Sanyam
(Not posting much)
My Blog: Yatantrika
Migrate to Standard C++ :When to tell your C++ Code is Non-Standard.
Please Read before posting: How To Ask Questions The Smart Way

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siddhant3s siddhant3s is offline

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Master Poster

Re: Help needed with Caesar Cipher

Apr 24th, 2009

Look, I coded the function myself and it is working great;
I will give you the code of the encrypter to get you started, you should write the decrypter yourself:

 Help with Code Tags 
 cpp Syntax (Toggle Plain Text) 
void CaesarEncrypt(char word[],int key,int size)
{
    for (int i=0;i<size;i++)
    {
        if (word[i] >='A' && word[i] <='Z')
        {
            int OV=word[i] + key;//overflow
 
            word[i]=(OV <= 'Z')? OV :'A' + (OV-'Z'-1);
        }
 
        if (word[i]<='z'&&word[i]>='a')
        {
           int OV=word[i] + key;//overflow
 
            word[i]=(OV <= 'z')? OV :'a' + (OV-'z'-1);
        }
 
    }
}
void CaesarEncrypt(char word[],int key,int size)
{
    for (int i=0;i<size;i++)
    {
        if (word[i] >='A' && word[i] <='Z')
        {
            int OV=word[i] + key;//overflow

            word[i]=(OV <= 'Z')? OV :'A' + (OV-'Z'-1);
        }

        if (word[i]<='z'&&word[i]>='a')
        {
           int OV=word[i] + key;//overflow

            word[i]=(OV <= 'z')? OV :'a' + (OV-'z'-1);
        }

    }
}