Caesar Cipher with Arrays

[Mch5904]

Hi, I am writing a program that decrypts a file input from the user. The user will have the option of using a caesar or substitution cipher. Right now, I have the caesar cipher done, but it will not run. Any help would be much appreciated! Thanks!

 #include <iostream>			//for standard I/O
#include <fstream>			//necessary for file input
#include <string>			//necessary for fileName input

using namespace std;

void PrintHeading ();			//prototype for printing the initial heading
char PrintMenu ();				//prototype for printing menu and gaining user's choice
void OpenFile (ifstream &);		//prototype for opening file 
void CeasarCypher (ifstream &);	//prototype for performing a caesar decryption
void SubCypher (ifstream &);	//prototype for performing a substitution decryption

typedef char alphabet[26];		//alphabet array with 26 elements


int main()
{
	char choice;			//input from user's menu choice
	ifstream inFile;		//necessary for opening file
	string fileName;		//needed for user to input name of file
	bool condition = true;	

	//call function that prints overall heading
	PrintHeading();	

	while(condition)
	{
		choice = PrintMenu();		//assign char from PrintMenu function to choice variable
		switch(choice)
		{
		case 'C':
		case 'c': cout << choice << endl;
				  OpenFile(inFile);
				  CeasarCypher(inFile);
			break;
		case 'S':
		case 's': cout << choice << endl;
				  OpenFile(inFile);
			break;
		case 'Q':						//if user wants to quit program
		case 'q': condition = false;	//set condition to false and print closing message
		cout << "***********************************************" << endl
			 << "\tThank you for using the DECRYPTER!" << endl
			 << "***********************************************" << endl << endl;
			break;
		default: cout << "No." << endl;
			break;
		}
		
	}

	return 0;	//return zero
}

void PrintHeading ()	//function that prints initial heading of decryption program
{ //PrintHeading function
	cout << "***********************************************" << endl
		 << "\t Welcome to The DECRYPTER!\t\t" << endl << endl
		 << " You have the option of performing either a" << endl
		 << "\t  Caesar decryption\t" << endl << "\t\t or \t\t" << endl
		 << "\tSubstitution decryption.\t" << endl << endl 
		 << " You will be asked for a file to be decoded." << endl << endl
		 << " The DECRYPTER will then echoprint one line of" << endl
		 << "  your encoded text from your specified file" <<endl
		 << "     followed by the same text decoded." << endl << endl
		 << "\t   Let's get started!" << endl 
		 << "***********************************************" << endl << endl << endl;
} //PrintHeading function

char PrintMenu ()		//function that displays menu and gathers user's choice as input
{ //PrintMenu function
	char menuChoice;	//character that user inputs as menu choice

	//prompt user for selection and gather input
	cout << "Which decryption method would you like to use?" << endl
		 << "To use the Caesar Cypher, please enter C." << endl
		 << "To use the Substitution Cypher, enter S." << endl
		 << "To quit the program, enter Q." << endl
		 << "Please enter your selection: ";	
	cin >> menuChoice;

	while(menuChoice != 'C' && menuChoice != 'c' && menuChoice != 'S' && menuChoice != 's' && menuChoice != 'Q' && menuChoice != 'q')
	{
		cout << "Please re-enter a valid menu choice: ";	//if selecition is not a valid menu choice
		cin.clear();										//clear and reprompt until valid choice is obtained
		cin >> menuChoice;
	}
	
	return(menuChoice);	//return user's menu choice
} //PrintMenu functionss

void OpenFile (ifstream & inFile)
{
	string fileName;
		cout << endl << "Please enter a valid file name (no blanks!) to decode: ";	//prompt for file name to be decrypted
		cin >> fileName;					//user inputs string for name of file

		inFile.open(fileName.c_str());		//if file exists, open it

		while(!inFile)						//if file does not exist
		{									//reprompt user until they input valid file name
			cout << "Sorry! That is not a valid file name! Please try again: ";
			cin >> fileName;			
			inFile.clear();
			inFile.open(fileName.c_str());
		}		
}

void CaesarCypher (ifstream & inFile)
{
	alphabet normal = {'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'};
	alphabet caesar;
	
	int digitcount = 0,linecount = 0,shift;
	char shiftval,decchar;
	
	bool matchfound = false;
	string temp;
	
	inFile.get(shiftval);
	if(inFile.peek() != '\n')
	{
		shift = (shiftval - '0')*10;
		inFile.get(shiftval);
		shift= shift + (shiftval - '0');
	}
	for(int i =0; i < 26; i++)
	{
		caesar[i] = normal[(i+shift)%26];   //make sure this gives correct alphabet values
	}
	//Print out heading here
	while(getline(inFile, temp))
	{
		cout << temp;
		for(int i = 0; i < temp.size(); i++)
		{
			for(int j = 0; j < 26; j++)
			{
				if(temp[i] == caesar[j])
				{
					decchar = normal[j];
					matchfound = true;
				}
			}
		if(!matchfound)
			cout << temp[i];
		else
			cout << decchar;
		}
		cout << endl;
		decchar = ' ';
		matchfound = false;
	}
	inFile.close();
}

[giblit]

There have been a lot of these recently. Basically a caesar cipher is a shift of 3 to the right. You seem to be doing a basic shift cipher. What you want to do is 1) check if it is a letter. If not go to step 5
2) make the letter upper or lower case
3) add the shift to the letter
4a) if the shift is positive(right) and greater than upper/lower case 'z' subtract 26.
4b) if the shift is negative(left) and less than upper/lower case 'a' add 26.
5) go to next character.

http://www.cplusplus.com/forum/beginner/128705/
http://www.cplusplus.com/forum/beginner/128695/

[Mch5904]

Thanks for the help.
I still don't see why this is not working(it has to be something in the CaesarCypher function though). The program is supposed to work with any shift and it must print the results like shown....
Also, this is what the output is supposed to look like:

************************************************
The DECRYPTER
of
Substitution Scheme Encryption
Using Caesar Substition set
************************************************


Original alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Shift Value: 6
Encrypted alphabet: GHIJKLMNOPQRSTUVWXYZABCDEF


ZNOY OY G YOSVRK ZKYZ ZU YKK
=> THIS IS A SIMPLE TEST TO SEE


OL ZNK VXUMXGS CUXQY. OL EUA
=> IF THE PROGRAM WORKS. IF YOU


IGT XKGJ ZNOY, ZNKT KBKXEZNOTM
=> CAN READ THIS, THEN EVERYTHING


OY UQ.
=> IS OK.

[giblit]

I'm not sure exactly I could figure it out but would take a little bit of time though I still think you are overly complicating the problem. Here is a very basic example:

//you know how to read in strings so just do this after reading in

for(char &it : str) //you can iterate anyway you want
{
    if(isalpha(it) && (it = toupper(it) + shift) && it > 'Z') //shifted right and out of bounds
         it -= 26;
}