import std.stdio : writeln;

​

/**

Shifts every character in the

array `input` for `shift` characters.

The character range is limited to `a-z`

and the next character after z is a.

​

Params:

    input = array to shift

    shift = shift length for each char

Returns:

    Shifted char array

*/

char[] encrypt(char[] input, char shift)

{

    auto result = input.dup;

​

    for (int i=0; i< result.length; i++) {

        char ch = result[i];

​

        int alphaIndex = ch - 'a'; // a -> 0, b -> 1, c -> 2, etc

​

        int shiftedIndex = (alphaIndex + shift) % 26; // 26 chars in alphabet

​

        int newValue = 'a' + shiftedIndex; // 0 -> a, 1 -> b, etc

​

        result[i] = cast(char)newValue;

    }

    return result;

}

​

void main()

{

    // We will now encrypt the message with

    // Caesar encryption and a

    // shift factor of 16!

    char[] toBeEncrypted = [ 'w','e','l','c',

      'o','m','e','t','o','d',

      // The last , is okay and will just

      // be ignored!

    ];

    writeln("Before: ", toBeEncrypted);

    auto encrypted = encrypt(toBeEncrypted, 16);

    writeln("After: ", encrypted);

​

    // Make sure we the algorithm works

    // as expected

    assert(encrypted == [ 'm','u','b','s','e',

            'c','u','j','e','t' ]);

}