caesar cipher help.

This is a discussion on caesar cipher help. within the C Programming forums, part of the General Programming Boards category; I want to add a few things to this caesar cipher program but am not exactly sure how. They are: ...

  1. #1
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    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;
    }
    Last edited by stormfront; 11-18-2005 at 05:00 PM.

  2. #2
    C++ Enthusiast jmd15's Avatar
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    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.
    Trinity: "Neo... nobody has ever done this before."
    Neo: "That's why it's going to work."
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  3. #3
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    Quote Originally Posted by jmd15
    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.

    thx, but i just want it to swap the first letter to the end.
    example: "hello" would be "elloh"
    Is there an easy way to implement this ?

  4. #4
    C++ Enthusiast jmd15's Avatar
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    Oh nevermind, I thought you wanted to swap the two.
    Trinity: "Neo... nobody has ever done this before."
    Neo: "That's why it's going to work."
    c9915ec6c1f3b876ddf38514adbb94f0

  5. #5
    ... kermit's Avatar
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    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.

    Give it a try, and post your code if you can't get it.

  6. #6
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    Is this what you wanted?

    Code:
    void swapit(char *pInput)
    {
        char b, e;
        b = pInput[0];
        e = pInput[strlen(pInput)-1];
        pInput[0] = e;
        pInput[strlen(pInput)-1] = b;
    }

  7. #7
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    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?
    Last edited by stormfront; 11-18-2005 at 05:57 PM.

  8. #8
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    Example...
    Code:
    #include <stdio.h>
    #include <string.h>
    
    void swapit(char *pInput)
    {
        char b, e;
        b = pInput[0];
        e = pInput[strlen(pInput)-1];
        pInput[0] = e;
        pInput[strlen(pInput)-1] = b;
    }
    int main(void)
    {
        char szSwap[] = {"Hello"};
        printf("%s\n", szSwap);
        swapit(szSwap);
        printf("%s\n", szSwap);
        return 0;
    }

  9. #9
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    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
    Last edited by stormfront; 11-18-2005 at 06:13 PM.

  10. #10
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    Possibly this???
    Code:
    #include <stdio.h>
    #include <string.h>
    char * swapit(char *pInput)
    {
       static char szTemp[128];
        char b;
        b = pInput[0];
        memset(szTemp, 0, sizeof szTemp);
        strcpy(szTemp,pInput+1);
        szTemp[strlen(szTemp)] = b;
        return  (szTemp);
    }
    int main(void)
    {
        char szSwap[] = {"Hello"};
        printf("%s\n", szSwap);
        printf("%s\n",swapit(szSwap));
        return 0;
    }

  11. #11
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    Thats it, but how do i get it to accept What the user inputs instead of hello?

  12. #12
    ... kermit's Avatar
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    Read the FAQ.

    ~/

  13. #13
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    im working on it...slowly
    Last edited by stormfront; 11-18-2005 at 07:02 PM.

  14. #14
    Frequently Quite Prolix dwks's Avatar
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    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?
    dwk

    Seek and ye shall find. quaere et invenies.

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  15. #15
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    No, still cant get it to work in the code. : (

    i know i must be trying to put it in the wrong place

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