caesar cipher help.

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.

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?

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.

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.

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

***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

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.

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

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.

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.