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.

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 ?

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

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.

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;
}

---

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?

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;
}

---

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

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;
}

---

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

Read the FAQ.

~/

:confused: 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?

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

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

Don't know if this is the most efficient way to do it but here's a WORKING EXAMPLE:

Code:

---

#include <cstdio>
#include <cstring>

void swapfront(char[]);

int main()
{
    printf("Enter word:");
    char word[256]={0};
    scanf("%s",&word);
    swapfront(word);
    printf("%s\n",word);
    return 0;
}
void swapfront(char word[])
{
    char f;
    f=word[0];
    char temp[256]={0};
    int i=1;
    for(int b=0;b<strlen(word);b++)
    {
    temp[b]=word[i];
    i++;
    }
    temp[strlen(word)-1]=f;
    strcpy(word,temp);
}

---

Once word is passed to the function swapfront, word now holds the new arrangement of characters.

Quote:

---

Originally Posted by jmd15

Don't know if this is the most efficient way to do it but here's a WORKING EXAMPLE:

---

How about one that compiles as C89? :p

Code:

---

scanf("%s",&word);

---

Bad gets imitation. And the & shouldn't be there.

Code:

---

for(int b=0;b<strlen(word);b++)

---

Don't use strlen(s) as a loop condition.

Quote:

---

Don't use strlen(s) as a loop condition.

---

It's very inefficient, looping through the whole string to find the NULL terminator for every loop of your loop.

Code:

---

printf("%s\n",word);

---

And that's like puts(). :)

And the header files are C++ ones. And variables are declared halfway through code blocks.

Quote:

---

Originally Posted by jmd15

Don't know if this is the most efficient way to do it but here's a WORKING EXAMPLE:

Code:

---

#include <cstdio>
#include <cstring>

void swapfront(char[]);

int main()
{
    printf("Enter word:");
    char word[256]={0};
    scanf("%s",&word);
    swapfront(word);
    printf("%s\n",word);
    return 0;
}
void swapfront(char word[])
{
    char f;
    f=word[0];
    char temp[256]={0};
    int i=1;
    for(int b=0;b<strlen(word);b++)
    {
    temp[b]=word[i];
    i++;
    }
    temp[strlen(word)-1]=f;
    strcpy(word,temp);
}

---

Once word is passed to the function swapfront, word now holds the new arrangement of characters.

---

Well heres what i have been having trouble with.
After i get input from the user in the encode function i have. I want it to switch the first letter to the last posistion as your code above does. Then complete the decode function.

Code:

---

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);

***switch first letter to last here***
       

        {       
                while ( buff[i] != '\0' )
                        {
                                buff[i] = buff[i] + 3;
                                i++;
                               
                        }
        }
                printf("\n Your encrypted text is: %s \n", buff);
}

---

Ive just been placing the function that does the switch below the decode function. But when i try to put the code that accepts input and calls the switch function i get errors. I have tried rearranging parts of it to fit with what i want to no avail. I hope this mad sense :confused:

Quote:

---

***switch first letter to last here***

---

You can do that like this:

Code:

---

size_t len = strlen(buff);
temp = buff[0];
buff[0] = buff[len];
buff[len] = temp;

---

[edit]
Never mind. That doesn't do what you want.

So you want to insert a call to swap_front() or what ever it is right there? Or what?

No, it doesn't "mad sense". :)
[/edit]

"mad sense" lol, i think im going mad trying to learn this stuff!

basically right after the word to be encoded is accepted in the encode function from the user i want to swap the first letter to the end. example: hello-elloh

Then complete the encode function.

also im getting these errors

error C2065: 'temp' : undeclared identifier

error C3861: 'temp': identifier not found, even with argument-dependent lookup

Quote:

---

Originally Posted by stormfront

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

---

Code:

---

#include <stdio.h>
#include <string.h>

char *foo(char *text)
{
  size_t len = strlen(text);
  char first = *text;
  memmove(text, text + 1, len - 1);
  text[len - 1] = first;
  return text;
}

int main(void)
{
  char mytext[] = "frog";
  puts(mytext);
  puts(foo(mytext));
  return 0;
}

/*
frog
rogf
*/

---

Man, Sorry! All the examples I have seen of scanf use it as I did. I'm not a C programmer but do know a bit of C, I use C++ so sorry about my technical errors. Sometimes I forget which board I'm on, you're lucky I didn't post C++ ;)

oooh, haha well im still workin on it, i need to get it done before tuesday cause thanksgiving is coming up and i wont have time to work on it. But, i still have a few days i guess.

Quote:

---

Originally Posted by stormfront

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.

---

Such that this might be an input/output pair?

Code:

---

hello world
kiqrv ExBwp

---

Quote:

---

Originally Posted by Dave_Sinkula

Such that this might be an input/output pair?

Code:

---

hello world
kiqrv ExBwp

---

---

yes, it would output what you have above. I know i need some kind of loop, but i am not sure how to do it because we havent learned very advanced looping in my class yet. ( i know it isnt a very advanced loop lol, but it is to me!)

So in other words:

Code:

---

letter = letter + k + loop_counter

---

Right? Now you should be able to figure out the implementation of this.


Quzah.

Quote:

---

Originally Posted by quzah

So in other words:

Code:

---

letter = letter + k + loop_counter

---

Right? Now you should be able to figure out the implementation of this.


Quzah.

---

Almost, i just dont know how to check each individual letter for the loop, we have done loops like this: for(something = 0, something < \0, something ++);

How would i check each individual letter of the text to be encoded to increase each letter by one?

Do you know how to go through each letter one at a time and print it? If so, you do the same thing, only you change it, or check it, or what not.

Code:

---

char buf[] = "Hello world!";
int x;
for( x = 0; buf[ x ] != '\0'; x++ )
{
    printf( "buf[ %d ] is %c\n", x, buf[ x ] );
}

---

Quzah.

got it! i'll get to work on it after class.

I can get anything to work , it just messes my code up even more, not even worth posting cause it is evidently way wrong. :(

Start simple. Make a program that reads an entire line. Compare that line with your phrase to stop looking on.

Code:

---

char buf[BUFSIZ] = {0};
FILE *fp;

fp = fopen( "yourfilename", "r" );
if( fp == NULL )
    ...exit the program or whatever...

while( fgets( buf, BUFSIZ, fp ) != NULL )
{
    if( strstr( buf, "searchforthisphraseinbuf" ) == 0 )
        ...break from the loop to stop reading the file...
}

---

Quzah.

hmm,


would something like this get me anywhere?

Code:

---

for( x = 0; buf[ x ] != '\0'; x++ )
{
    if ((buf[x]>='A') && (buf[x]<='Z'))
    {
      something = 'A' + ((buf[x]-'A')+( something?? + x))%26;
    }
}

---

just to get me started.

ok, im not getting anywhere with this so im concentrating on getting the alphabet to wrap around and letting the user choose the number to encode by.

I have it where the user can choose the number and it works, but it places funny characters at the end of my words. I started trying to get the alphabet to wrap around but im getting erros can someone tell me whats wrong.

Code:

---

void encode ( void )
{
        char buff[BUFSIZ];
        int i = 0;
        int shift_value;

    printf( "Doing encrypt\n" );
        printf("\nPlease enter the text you wish to encrypt: ");
        fgets(buff, sizeof(buff), stdin);
        if ("%s"  > 'Z')
        {
          "%s" -= 'Z' - 'A';
        }
        printf("\nEnter your encryption shift value (anything from +-1 to 25): ");
    scanf ("%i", &shift_value);
       
       

        {       
                while ( buff[i] != '\0' )
                        {
                                buff[i] = buff[i] + shift_value;
                                i++;
                               
                        }
        }
                printf("\n Your encrypted text is: %s \n", buff);
}

---

thats my encode function where i let the user choose the encode value, and it is also where im trying to wrap the alphabet around.

Quote:

---

Originally Posted by quzah

So in other words:

Code:

---

letter = letter + k + loop_counter

---

Right? Now you should be able to figure out the implementation of this.


Quzah.

---

OMG that was so easy, ok, i figured this part out.

IS there an easy way like that that i can move the first letter of the stuff to be encoded to the end? The things people have been posting are confusing the heck out of me.

Quote:

---

IS there an easy way like that that i can move the first letter of the stuff to be encoded to the end?

---

Hint: strlen() returns the length of a string. Using

Code:

---

buffer[strlen(buffer)-1]

---

will access the last character in the string.

Here is something else to look at, although looking at it again after being a way a while it does look rather hideous.

Code:

---

char *bar(char *text)
{
  static const char alpha[][26] =
  {
      "ABCDEFGHIJKLMNOPQRSTUVWXYZ",
      "abcdefghijklmnopqrstuvwxyz",
  };
  char *start = text;
  int n, k = 3;
  for ( ; *text; ++text )
  {
      if ( isalpha(*text) )
      {
        int set = islower(*text) ? 1 : 0;
        n = strchr(alpha[set], *text) - alpha[set] + k++;
        if ( n >= sizeof alpha[0] )
        {
            *text = alpha[!set][n % sizeof alpha[0]];
        }
        else
        {
            *text = alpha[set][n];
        }
      }
  }
  return start;
}

---