Caesar Cipher

[Ariamn]

Heya, need a tad help or input with my Caesar cipher program, what seems to be the issue is that when I input xzy, or if characters exceed the final alphabet character 'z' it creates strange symbols instead, such as [/].

Anyone kind enough to give me a hint? :)

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string input;
    int length;
    int shift;
    int decenc;
    cin >> decenc;
    cin >> shift;
    cin.ignore();
    getline(cin, input);

    length = (int)input.length();

    for (int count = 0; count < length; count++)
    {
        if (isalpha(input[count]))
        {
            if(decenc == 1)
            {
                for (int i = 0; i < shift; i++)
                {
                    input[count] = toupper(input[count]);

                    if (input[count] == 'z')
                    {
                        input[count] = 'a';
                    }

                    else
                    {
                        input[count]++;
                    }
                }
            }

            if(decenc == 2)
            {
                for (int i = 0; i < shift; i++)
                {
                    input[count] = tolower(input[count]);

                    if (input[count] == 'a')
                    {
                        input[count] = 'z';
                    }

                    else
                    {
                        input[count]--;
                    }
                }
            }
        }
    }
    cout << input;
}

[Ariamn]

So hmm, maybe I should include how my program works first.

first input decides if you want to encrypt or decrypt a message (1 for decrypt and 2 for encrypt)

and second input is how far you want to push back the letters.

third input would be the message you want to encrypt/decrypt.

So, with that, I seem to hit a snag because there are certain "symbols"(e.g [ / ] )  there that are not supposed to be included in the program.

For instance,
if I input:

1
25
Attack at dawn

It produces: ZMMZ/D ZM [ZPG

but more desired output would be without the symbols.

[ne555]

                    input[count] = toupper(input[count]);
                    if (input[count] == 'z') //¿how this could ever happen? 

[Ariamn]

it seems to be working in some cases, if it exceeds 'z', it will continue to go through the start of the alphabet, i.e 'a'.

or so is the initial thought.

[Ariamn]

Ok, so you were right, it doesn't do jack, how do I fix this?

I've been trying to include something like another while loop but it doesn't seem to be functioning correctly.

Any ideas, anyone?

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string input;
    int length = 0;
    int shift = 0;
    int decenc = 0;

    cin >> decenc;
    cin >> shift;
    cin.ignore();

    getline(cin, input);

    length = (int)input.length();

    //while(getline(cin, input))
    {
        for (int count = 0; count < length; count++)
        {
            if (isalpha(input[count]))
            {
                if(decenc == 1)
                {
                    for (int i = 0; i < shift; i++)
                    {
                        input[count] = toupper(input[count]);
                        {
                            input[count]++;
                        }
                    }
                }

                if(decenc == 2)
                {
                    for (int i = 0; i < shift; i++)
                    {
                        input[count] = tolower(input[count]);
                        {
                            input[count]--;
                        }
                    }
                }
            }
        }

        cout << input;
    }
}

my current code.

[JLBorges]

Use the standard library?

#include <iostream>
#include <string>
#include <algorithm>
#include <cctype>

// return the character unchanged if the character is not in the aplphabet
char encrypt( char c, const std::string& alphabet, const std::string& cipher )
{
    auto pos = alphabet.find(c) ;
    return pos != std::string::npos ? cipher[pos] : c ;
}

int main()
{
    const std::string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" ;

    constexpr std::size_t shift_by = 5 ; // instead, read from stdin if required

    std::string cipher = alphabet ;
    // shifts right; use cipher.begin(), cipher.begin()+shift_by for left shift
    std::rotate( cipher.rbegin(), cipher.rbegin()+shift_by, cipher.rend() ) ;

    std::string phrase ;
    while( std::getline( std::cin, phrase ) )
    {
        for( char& c : phrase )
            std::cout << encrypt( std::toupper(c), alphabet, cipher ) ;
        std::cout << '\n' ;
    }
}

[Ariamn]

auto is not working with my current compiler for some reason, produces some juicy errors (codeblocks)

I'm thinking, maybe stick with my current, but if all else fails, I will check out that one, thanks JL

[JLBorges]

> auto is not working with my current compiler for some reason,

You need to enable C++11 support:

In CodeBlocks,
Menu => Settings => Compiler... Compiler settings =>Compiler Flags

check -std=c++11

While you are at it, also check -Wall, -Wextra and -pedantic-errors

[Ariamn]

Solved!

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string input;
    int length = 0;
    int shift = 0;
    int decenc = 0;

    cin >> decenc;
    cin >> shift;
    cin.ignore();

    getline(cin, input, '\0');

    length = (int)input.length();


    {
        for (int count = 0; count < length; count++)
        {
            if (isalpha(input[count]))
            {
                if(decenc == 1)
                {
                    for (int i = 0; i < shift; i++)
                    {
                        input[count] = toupper(input[count]);
                        if(input[count] == 'Z')
                            (input[count] = 'A');
                        else
                        {
                            input[count]++;
                        }

                    }
                }

                if(decenc == 2)
                {
                    for (int i = 0; i < shift; i++)
                    {
                        input[count] = tolower(input[count]);
                        if(input[count] == 'a')
                        (input[count] = 'z');
                        else
                        {
                            input[count]--;
                        }
                    }
                }
            }
        }
        cout << input;
    }
}