This message was edited by beetle17 at 2006-11-20 8:31:30

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This message was edited by beetle17 at 2006-11-20 8:24:43

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l just learn C program not long time ago,it is too diffcult for me to write a cipher

(Plaintext : a nice day)
(Key : -3)
(Ciphertext : X kfZb aXv)

Cipher will accept commands from the user and perform the operations required by the commands. There are three different commands. Key command starts with "K1:"followed by a string as the key. Encryption command starts with "E1:" followed by the plaintext. Decryption command starts with "D1:" followed by the ciphertext to be decrypted. After the user inputs an encryption (or decryption) command, Cipher1 should encrypt the plaintext (or decrypt the ciphertext) using the key input by a previous key command, and print the results. The error message "key not found" should be printed if the user inputs an encryption or decryption command before a key command. If the user
inputs multiple keys, the latest key will be used in the following encryption/decryption operations. Below are two examples (underlined text is the input from the user, and italic text is the output of Cipher).
When the plaintext/ciphertext includes non-letter symbols, Cipher1 will ignore them.For example, a plaintext of "No. 2" is equivalent to "No".

Example I of Cipher:
K 1: 3
E 1: I like dogs
C i p h e r t e x t is < L olnh grjv >
D 1: L olnh grjv
P l a i n t e x t i s < I like dogs >
E 1: H e l l o
C i p h e r t e x t i s < Khoor >

Example II of Cipher:
E 1: I like dogs
K e y not found
K 1: -54
E 1: Hello
C i p h e r t e x t is < Fcjjm>
K 1: h h h h
Invalid K e y

This message was edited by beetle17 at 2006-11-20 23:38:22

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l am typeing a program about cipher ,
to make the result:
Example I of Cipher:
input K 1: 3
//P l a i n t e x t &#61453; i s < I &#61453; l i k e &#61453; d o g s >
input E 1: I &#61453; l i k e &#61453; d o g s
//Ciphertext is < L &#61453; o l n h &#61453; g r j v >
output D 1: L &#61453;o l n h g r j v
input K 1: h h h h
putput Invalid &#61453; K e y

where K1: , D1: ,E1: are 3 different command,
Key command starts with "K1:"followed by a string as the key.
Encryption command starts with "E1:" followed by the plaintext.
Decryption command starts with "D1:" followed by the ciphertext to be decrypted.

l want to ask how could l write to separate K1: , D1: ,E1:from the input string,to let make appling different function on different command.

l only write
#include<stdio.h>
#include<string.h>
main()
{
char sen[100], x[100],k[100];command[]={'sen[0]','sen[1]','sen[2]','\0'}
int i, key;
gets(sen);
switch(command[]){
case "K1:":
function A;
case "D1:":
function B;
case "E1:":
function C;
default:
printf(input error)
}
is it Ok?