Having heard you have gotten really good at programming, your friend has come to
ID: 3860225 • Letter: H
Question
Having heard you have gotten really good at programming, your friend has come to ask for your help with a simple task. She would like you to implement a program to encrypt the messages she exchanges with her friends.
The idea is very simple. Every letter of the alphabet will be substituted with some other letter according to a given key pattern like the one below.
"abcdefghijklmnopqrstuvwxyz"
"doxrhvauspntbcmqlfgwijezky" // key pattern
For example, every 'a' will become a 'd' and every 'k' will become a 'n'. Upper case letters are encoded the same way but they remain upper case (e.g. every 'A' will become a 'D'), while any characters which are not letters of the alphabet (e.g.: digits, space, punctuation, etc) remain as given (e.g. every '1' remains a '1'). The process is symmetrical so decoding of an encoded text can be done using the corresponding decoding key pattern.
Part 1: You will implement a simple encoder class which encodes strings based on a key pattern. The class has a single public function to encode a string since decoding can be done using a new encoder constructed with the symmetrical decoding key pattern.
Part 2: Your friend is pretty happy with your program but she needs an improvement. She uses a lot of common abbreviations like “LOL” when she IMs her friends and she is worried sooner or later someone will figure out the whole scheme once they notice “TMT” appearing so often in the logs.
You plan to implement a new encoder which is based on the previous one but which has the ability to pad each character with a fixed number of random letters/digits. For example, with a padding of 3, “LOL” would be encoded to a word like T###M###T### where the # are random chars from the set [a-z, A-Z, 0-9], for example TabiM8rcTyFp or ThV9MbolTJDj, each time appearing different.
The padding encoder has a new function used to decode which removes the junk characters from the encrypted texts. This way LOL can be retrieved from both TabiM8rcTyFp and ThV9MbolTJDj since LabiO8rcLyFp and LhV9ObolLJDj are not very funny :)
A sample output of the program for the string "Hello class!" is given below:
Encoded: Uhttm xtdgg!
Decoded: Hello class!
Pad Encoded: UfTohAlrty44tqiTm2OG 95Kx3zgtrNQd1GrgD5PgKQu!koU
Pad Decoded: Hello class!
Explanation / Answer
the attachment is not opening. hence just pasting the encoding method.
void encode(char *input,char *output){
char encode_small[26] = {'d','o','x','r','h','v','a','u','s','p','n','t','b','c','m','q','l','f','g','w','i','j','e','z','k','y'};
char encode_cap[26] = {'D','O','X','R','H','V','A','U','S','P','N','T','B','C','M','Q','L','F','G','W','I','J','E','Z','K','Y'};
int i,n=strlen(input);
for(i=0;i<n;i++){
if(isalpha(input[i])){
if(isupper(input[i])){
output[i] = encode_cap[input[i]-'A'];
}else{
output[i] = encode_small[input[i]-'a'];
}
}
else{
output[i] = input[i];
}
}
output[i] = '';
}
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