by Given a string ‘s’ and a number ‘n’, write a function that returns a string with each character in s replaced with another character that is ‘n’ positions down the alphabet.
For example:
- If n is 1, A is replaced with B, B is replaced with C and so on.
- If n is 2, A is replaced with C, B is replaced with D and so on.
- If n is 3, X is replaced with A, Y is replaced with B and so on.
Algorithm
- Check passed value “n”. If it is greater than 26 then apply modulo function with 26. As after 26, replacement will always be repeated.
- Iterate through each character in given string.
- add the number “n” to the input character.
- if new character ASCII value is greater than “Z” then subtract 26 from it and save it.
- Save the string in output character array.
Let’s have a look into the sample code.
void string_encoder (const char* input, int n, char* output)
{
int len = strlen (input);
if (len == 0) {
cout << "Empty String Received !!" << endl;
return;
}
int mod_n = n % 26;
for (int i = 0; i < len; i++) {
output[i] = input[i] + mod_n;
if (output[i] > 'Z') {
output[i] = output[i] - 'Z' + 'A' - 1;
}
}
}
Define a function to convert back the encoded string to original string
Here we will define a function which will take the output string from the previous section and convert it back to original string.
Algorithm
- Check passed value “n”. If it is greater than 26 then apply modulo function with 26. As after 26, replacement will always be repeated.
- Iterate through each character in given string.
- subtract the number “n” to the input character.
- if new character ASCII value is lesser than “A” then add 26 to it and save it.
- Save the string in output character array.
Let’s have a look into the sample code.
void string_decoder (const char* output, int n)
{
int len = strlen (output);
if (len == 0) {
cout << "Empty String Received !!" << endl;
return;
}
int mod_n = n % 26;
for (int i =0; i < len; i++) {
char c = output[i] - mod_n;
if (c < 'A') {
c = 'Z' - ('A' - c) + 1;
}
cout << c;
}
cout << endl;
}
Let’s look into a main function which utilizes both the functions.
int main ()
{
char str[50] = {0};
char output[50] = {0};
int n = 0;
cout << "Input String " << endl;
cin >> str;
cout << "Input value of n" << endl;
cin >> n;
cout << "Input String: " << str << endl;
string_encoder (&str[0], n, &output[0]);
cout << "Encoded String: " << output << endl;
cout << "Decoded String: " ;
string_decoder (output, n);
}
Let’s analyze the output of above main function.
Input String
ACF
Input value of n
1
Input String: ACF
Encoded String: BDG
Decoded String: ACF
----------------------------------------------------------
Input String
AXZ
Input value of n
1
Input String: AXZ
Encoded String: BYA
Decoded String: AXZ
----------------------------------------------------------
Input String
AGI
Input value of n
26
Input String: AGI
Encoded String: AGI
Decoded String: AGI
----------------------------------------------------------
Input String
AXY
Input value of n
27
Input String: AXY
Encoded String: BYZ
Decoded String: AXY
