Thread: caesar cipher help.

I want to add a few things to this caesar cipher program but am not exactly sure how. They are:

1. Before encryption move the first letter of the message to the last posistion.( "frog" would be "rogf")

2.replace each letter by a constantly increasing value of k. So,
if k is 3, replace the first letter of the message by the letter that comes 3 positions after it. Next,
replace the second letter of the message by the letter that comes 4 positions after it. Next, replace
the third letter of the message by the letter that comes 5 positions after it, and so on.

3.At the beginning ask the user the value they want to use to encrypt the code. (It is currently set up at 3) But, i want it to be an option for the user.

4. Let the code "wrap around" when i type in zebra instead of returning cheud, it gives a funky character for z.

Not sure how to do these, they seem simple i just cant come up with how to do them.

Code:

#include <stdio.h>

void menu ( void ) {
    printf("Please enter a number: \n"
           "1-Encrypt\n"
           "2-Decrypt\n"
           "3-Exit\n"
           "prompt > ");
    fflush( stdout );
}

int getchoice ( void ) {
    char buff[BUFSIZ];
    int  choice = 0;
    do {
        menu();
        if ( fgets( buff, sizeof buff, stdin ) != NULL ) {
            /* success reading a line, does it make sense? */
            if ( sscanf( buff, "%d", &choice ) != 1 ) {
                printf( "Enter a number\n" );
            }
        } else {
            /* user EOF, just exit now */
            choice = 3;
        }
    } while ( choice < 1 || choice > 3 );
    return choice;
}

void encode ( void ) 
{
	char buff[BUFSIZ];
	int i = 0;
                printf( "Doing encrypt\n" );
	printf("\nPlease enter the text you wish to encrypt: ");
	
	fgets(buff, sizeof(buff), stdin);
	{	
		while ( buff[i] != '\0' )
			{
				buff[i] = buff[i] + 3;
				i++; 
				
			}
	}
		printf("\n Your encrypted text is: %s \n", buff);
}
void decode ( void ) 
{
	char buff[BUFSIZ];
	int i = 0;
                printf( "Doing decrypt\n" );
	printf("\nPlease enter the text you wish to decrypt: ");
	
	
	fgets(buff, sizeof(buff), stdin);
	{
		while ( buff[i] != '\0' ) 
			{
				buff[i] = buff[i] - 3;
				i++;
			}
	}
		printf("\nYour decrypted text is: %s \n", buff);
}

int main ( ) {
    int choice;
    while ( (choice=getchoice()) != 3 ) {
        if ( choice == 1 ) {
            encode();
        } else
        if ( choice == 2 ) {
            decode();
        }
    }
    return 0;
}

In the include file algorithm, there are many useful functions that could help you. One of these being swap(). Used as such:

Code:

....
    char msg[25]={0};
    strcpy(msg,"Hello");
    swap(msg[0],msg[(strlen(msg)-1)]);

Now instead of msg holding Hello it will hold oellH. I would also check out some of the other algorithms available.

Oh nevermind, I thought you wanted to swap the two.

that appears to be what i need but when i try to put it in my code and call it, it doesnt do anything....maybe im doing wrong. Where does it go?

hmm, no im still getting oellH using the swap function.

"Just use a loop and walk through your array replacing each current element with what is in the current element + 1. Of course you will want to save the original value of element 0 in a temp variable, and then when you are done 'shifting' all of your characters, you will want to place the character in temp in the last position in your array."


this seems like my best bet

im working on it...slowly

Code:

char szSwap[] = {"Hello"};

You don't need the curly braces.

Code:

static char szTemp[128];
    char b;
    b = pInput[0];
    memset(szTemp, 0, sizeof szTemp);

You can just use ={0}.

Did you get it to work, stormfront?