Ceasar Cipher

[slynoodle]

I am having some serious trouble! I have written some code and had some help with it, but I can figure out how to, with the current code, to take in a large text file and run the decryption. Here is the code I have come up with. I feel like it's clunky and not particularly efficient. sorry! Please Help!

 

#include <iostream>
#include <string>
#include <cstring>
#include <fstream>

using namespace std;


void Caesar(string& phrase, int shift);
int find_the_e(string phrase);

int main(){
	int shift = 0;
	string inputFileName;
	ifstream inputFile;
	string reply;
	char character;

	string phrase = "I am having a hard time wiht the file I/O"; 
	
	Caesar(phrase, shift);
	cout << "Encrypted Phrase: " << phrase << endl << endl;

	shift = find_the_e(phrase); //Find the most common letter
	cout << endl << "Most common letter was - " << (char)(4-shift+97) << " - so shifting " << shift << endl << endl;

	Caesar(phrase, shift);
	cout << "Translated Phrase: " << phrase << endl << endl;

	cin.sync();
	cin.get();
	return 0;
}

int find_the_e(string phrase){

	int letters[26];
	int highest = 0;
	char a = 'a';
	for(int i = 0; i < 26; ++i)
	letters[i] = 0;

	for(int i = 0; i < phrase.size(); ++i){
		if(isalpha(phrase[i])){
			letters[(int)tolower(phrase[i])-97]++;
		}
	}

	for(int i = 0; i < 26; ++i, ++a){
		if(letters[i] > letters[highest])
		highest = i;
	}

	return 4-highest;
}

void Caesar(string& phrase, int shift){
if(shift > 0){
	for(; shift > 0; --shift){
		for(int i = 0; i < phrase.size(); ++i){
			if(phrase[i] == 'z'){
				phrase[i] = 'a';
				continue;
			}
		else if(phrase[i] == 'Z'){
				phrase[i] = 'A';
				continue;
			}

	if(isalpha(phrase[i]))
	phrase[i]++;
		}
	}
}

else if(shift < 0){
	for(; shift < 0; ++shift){
		for(int i = 0; i < phrase.size(); ++i){
			if(phrase[i] == 'a'){
				phrase[i] = 'z';
				continue;
			}
		else if(phrase[i] == 'A'){
			phrase[i] = 'Z';
			continue;
		}

	if(isalpha(phrase[i]))
	phrase[i]--;
		}
	}
}

else return;
}