Caesar Cipher

[ketnav]

Hi guys, I have written a "Caesar cipher" code but I've been stuck since 2 days trying to work out why the section of my code that is supposed to increment the alphabet is not working...

  #include<iostream>
#include<string>

using namespace std;

string Encrypt(string&, int &);// Function Prototype.  This declares Encrypt to be a function that needs one variable as string and another as integer as arguments. Reference operator & in prototype

int main()
{

	string text;//the string that holds the user input

	int key;//key holds the number by which the user wants the alphabets to be shifted

	cout << "Enter your phrase: " << endl;
	getline(cin, text);//gets the user input ( including spaces and saves it to the variable text)

	cout << "Please choose a number(key) for which you wants the alphabets to be shifted:  " << endl;
	/*Note: the key can either be positive (forward shifting), negative (backward shifting) or zero (no shifting)*/

	cin >> key;//User input for number by which alphabets are going to be shifted


	cout << "Encrypted Message: " << Encrypt(text, key) << endl;//Function call to display encrypted message


	//system("Pause");

	return 0;
}



string Encrypt(string& Source, int& c)
{
	char fUpperCase[26] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };//Initialization of class member
	char fLowerCase[26] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' };//Initialization of class member

	int z;//z holds the value (int) of the length of the user input ( including spaces)
	z = (int)Source.length();	/*give the variable z the value of the user input length and length is normally an unsigned long integer hence
								we have to typecast it*/

	/*counter that makes it keep looping until it "encrypts" all of the user input (that's why it keeps looping while its less than z)*/
	for (int i = 0; i < z; i++)
	{
		for (int j = 0; j < 26; j++)
		{
			if (Source[i] == fLowerCase[j] || Source[i] == fUpperCase[j])
			{
				//text[i] = fLowerCase[j];

				if (c > 0)
				{
					//another counter that loops forwards key times by incrementing method
					for (int counter = 0; counter < c; counter++)
					{
						/*it checks if the letter text[x] is 'z' and if it is 'z' it will make it 'a'*/
						/*if (Source[i] == 'z')
						{
							Source[i] = 'a';
						}

						else if (Source[i] == 'Z')
						{
							Source[i] = 'A';
						}*/

						//else
						//{
							Source[i]++;
						//}

					}
				}

				else	if (c < 0)
				{
					//another counter that loops backwards key times by decrementing method
					for (int counter = 0; counter < abs(c); counter++)
					{
						/*it checks if the letter text[x] is 'a' and if it is 'a' it will make it 'z'*/
						if (Source[i] == 'a')
						{
							Source[i] = 'z';
						}

						else if (Source[i] == 'A')
						{
							Source[i] = 'Z';
						}

						else
						{
							Source[i]--;
						}
					}
				}

				else
				{
					Source[i];//No alphabet shifts
				}

			}

		}

	}

	return Source;
}

when I write 'c' as character it gives me a symbol '{' when the key is 1...when I change Source[i]++ to Source[i]-- if the key is greater than 0 for e.g 1 then the code strangely works it gives me 'b' character!!!!

[cire]

Have you walked yourself through the logic? Like say when the Source is "a" and c is 1? It should become obvious fairly quickly where you have some problems.

[ketnav]

Yes, when source is "a" and c is 1 it gives me a symbol '{' whereas if I change line 70 to source[i]-- it works, the code is working for decrement but not increment!!!

[ketnav]

Please help required....

[whitenite1]

@ketnav

Here's the program, greatly shortened. I added in a space, and divided the upper and lower case alphabets. Look it over and you should see how it works. I you have questions, just ask.

#include<iostream>
#include<string>

using namespace std;

string Encrypt(string&, int c);// Function Prototype.  This declares Encrypt to be a function that needs one variable as string and another as integer as arguments. Reference operator & in prototype

int main()
{

	string text;//the string that holds the user input

	int key;//key holds the number by which the user wants the alphabets to be shifted

	cout << "Enter your phrase: " << endl;
	getline(cin, text);//gets the user input ( including spaces and saves it to the variable text)

	cout << "Please choose a number(key) for which you wants the alphabets to be shifted:  " << endl;
	/*Note: the key can either be positive (forward shifting), negative (backward shifting) or zero (no shifting)*/

	cin >> key;//User input for number by which alphabets are going to be shifted


	cout << "Encrypted Message: " << Encrypt(text, key) << endl; //Function call to display encrypted message

	return 0;
}



string Encrypt(string& Source, int c)
{
	int i, j,letter;
	char fUpperCase[27] = { ' ', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };//Initialization of class member
	char fLowerCase[27] = { ' ', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};//Initialization of class member
	string cipher = "";
	int z = Source.length();	
	
	for (i = 0; i < z; i++)
	{
		for (j = 0; j < 27; j++)
		{
			if (Source[i] == fLowerCase[j])
			{
				letter = j + c;
					if (letter > 27) // If found letter + key is greater than array size
					letter -= 27; // Subtract 27 to start from array beginnings
				cipher += fLowerCase[letter];
			}
			else if (Source[i] == fUpperCase[j])
			{
				letter = j+c; 
				if (letter > 27)
					letter -=27;
				cipher += fUpperCase[letter];
			}
		}
	}
return cipher;
}

[ketnav]

But what was the problem in my code...Why I was not able to increment in line 70? but I could decrement...

[ketnav]

Somebody please tell me why I can'y increment my characters properly line 70??

[whitenite1]

@ketnav

No, I'm sorry, but cannot figure out the reason it doesn't increment properly. I would guess it's the logic of the loop. Not positive, but just guessing.

Here it is improved. It didn't check for negative numbers before..

#include<iostream>
#include<string>

using  std::cout;
using  std::cin;
using  std::endl;
using  std::string;

string Encrypt(string Source, int c);// Function Prototype.  This declares Encrypt to be a function that needs one variable
// as string and another as integer as arguments. Reference operator & in prototype

int main()
{
	string text;//the string that holds the user input
	int key;//key holds the number by which the user wants the alphabets to be shifted

	cout << "Enter your phrase: " << endl;
	getline(cin, text);//gets the user input ( including spaces and saves it to the variable text)

	cout << "Please choose a number(key) for which you wants the alphabets to be shifted:  " << endl;
	/*Note: the key can either be positive (forward shifting), negative (backward shifting) or zero (no shifting)*/

	cin >> key;//User input for number by which alphabets are going to be shifted

	cout << "Encrypted Message: " << Encrypt(text, key) << endl; //Function call to display encrypted message

	return 0;
}

string Encrypt(string Source, int c)
{
	int i, j,letter;
	char fUpperCase[27] = { ' ', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 
		'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };//Initialization of class member

	char fLowerCase[27] = { ' ', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
		'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};//Initialization of class member
	string cipher = "";
	int z = Source.length();	
	
	for (i = 0; i < z; i++)
	{
		for (j = 0; j < 27; j++)
		{
			if (Source[i] == fLowerCase[j])
			{
				letter = j + c; 
				if (letter > 27) // If found letter + key is greater than array size
						letter -= 27; // Subtract 27
				if (letter < 0) // If found letter - key is less than 0
						letter += 27; // Add 27
				
				cipher += fLowerCase[letter];
			}
			else if (Source[i] == fUpperCase[j])
			{
				letter = j + c; 
				if (letter > 27) // If found letter + key is greater than array size
						letter -= 27; // Subtract 27
				if (letter < 0) // If found letter - key is less than 0
						letter += 27; // Add 27
			
				cipher += fUpperCase[letter];
			}
		}
	}
	return cipher;
}