Converting space character in string to integer

**boostage** · 10-19-2006

Hi all. I am currently trying to write a program that implements the Ceasar cypher, which shifts all the letters in a message a certain number of letters forward. The way I am doing this is turning each letter into its ASCII number via static_cast-ing, doing a numerical formula to apply the shift, and then changing the new numbers back into letters to get the encrypted letter.
This worked fine for letters, but the problem is, I would like it to leave spaces (' ') alone, encrypting only letters themselves and leaving the spaces in the same spots. To do this, I say (where plaintext[i] is the original letter and cyphertext[i] is the new letter):

if (plaintext[i] == ' ')
cyphertext[i] = ' ';
else
//numerical formula for encrypting letters

However, it is not working at all. It ends up converting spaces into letters or symbols. Is there some wierd issue that I am not aware of forbidding comparisons with blank space? Any suggestions for how to fix this would be greatly appreciated. Thanks.

**nadroj** · 10-19-2006

does it work if you compare it to 32, its decimal value

**boostage** · 10-19-2006

I already tried that, and it apparently never registered as being equal to 32 when I input spaces.

**nadroj** · 10-19-2006

could you post as much relevant code (or all if not too much) for us to check out

**boostage** · 10-19-2006

Code:

for (int i = 0; i < len; ++i) {     //will cycle through all the letters of the message
        if (plaintext[i] == ' ') //ERROR HERE
            cyphertext[i] = ' ';
        else
            numtrans[i] = static_cast<int>(plaintext[i]);   //converts message letters to numbers
            numtrans[i] = ((numtrans[i] - 65 + keyshift) % 26) + 65;     //encyphers
            cyphertext[i] = static_cast<char>(numtrans[i]);     //converts back into letters, shifted
    }

This is the piece of code I used to convert letters to numbers, encode them, then convert back. The only actual error is in the second line, where I am checking to see whether plaintext[i] is a blank space, but the rest of the code is included because it might be relevant. Note: len is the length of the string plaintext, and numtrans is an integer array to hold the numerical values of the letters.

I tried replacing

Code:

if (plaintext[i] == ' ')

with

Code:

if (static_cast<int>(plaintext[i]) == 32)

but it did not help.

**boostage** · 10-19-2006

Wait all, I am sorry, I found the error in my code. It was actually fairly trivial. I just left out some brackets after the "else" statement above, but since the space was the only thing acting up, I thought that was the error. My code is working fine now.

**Dave_Sinkula** · 10-19-2006

For whatever reason, I was just writing a Caesar recently. FWIW as something to compare with:

Code:

#include <ctype.h>

/**
 * Encode text using a Caesar cipher. Only alphabetic characters are encoded,
 * and in their original case (upper or lower).
 *
 * @param  text   pointer to the text to encrypt
 * @param  shift  the number of characters to shift (must be less than 26)
 *
 * @return pointer to the encoded text
 *
 * @example
 * <pre>char text[] = "All work and no play makes Jack a dull boy.";
 * puts(text);            // "All work and no play makes Jack a dull boy."
 * puts(caesar(text, 3)); // "Doo zrun dqg qr sodb pdnhv Mdfn d gxoo erb."</pre>
 *
 * @note http://en.wikipedia.org/wiki/Caesar_cipher
 */
char *caesar(char *text, size_t shift)
{
    static const char alpha[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    char *start = text;
    size_t i, j;
    for ( i = 0; text[i]; ++i )
    {
        for ( j = 0; alpha[j]; ++j )
        {
            if ( toupper(text[i]) == alpha[j] )
            {
                char encoded = alpha[(j + shift) % (sizeof alpha - 1)];
                text[i] = islower(text[i]) ? tolower(encoded) : encoded;
                break;
            }
        }
    }
    return start;
}

(C, of course.)

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