The program below encodes a number using the formula below with a secret key:

encoded number $=($original number $+$ key$)$ x $5$

#include

using namespace std;

$//$ Your code for A$2$ should be inserted here

int main$()\{$

Encoder eKey$(123)$;

int encodedValue, decodedValue;

int value $=31$;

cout $<<$ "original value: $"<<$ value $<<$ endl;

encodedValue $=$ eKey.encode$($value$)$;

cout $<<$ "encoded value: $"<<$ encodedValue $<<$ endl;

decodedValue $=$ eKey.decode$($encodedValue$)$;

cout $<<$ "decoded value: $"<<$ decodedValue $<<$ endl;

return $0$;

$\}$

Sample output:

original value: $31$

encoded value: $770$

decoded value: $31$

Implement the Encoder class with the following:

$($a$)$ The class scope with appropriate access specifier labels. $(2$ marks$)$

$($b$)$ A private data member key $($integer$).(2$ marks$)$

$($c$)$ A default constructor that initializes the value of key to $3.(4$ marks$)$

$($d$)$ A constructor with ONE parameter, that initializes the value of key with the argument.

$(4$ marks$)$

$($e$)$ A public member function encode$()$ that takes a number $($integer$)$ as parameter, and returns

the encoded number $($integer$)$ using formula above with the key value. $(4$ marks$)$

$($f$)$ A public member function decode$()$ that takes a number $($integer$)$ as parameter, and returns

the decoded number $($integer$)$ using the key value. $(4$ marks$)$