exercism-solutions/cpp/crypto-square/README.md

Crypto Square

Implement the classic method for composing secret messages called a square code.

The input is first normalized: The spaces and punctuation are removed from the English text and the message is downcased.

Then, the normalized characters are broken into rows. These rows can be regarded as forming a rectangle when printed with intervening newlines.

For example, the sentence

If man was meant to stay on the ground god would have given us roots

is 54 characters long.

Broken into 8-character columns, it yields 7 rows.

Those 7 rows produce this rectangle when printed one per line:

ifmanwas
meanttos
tayonthe
groundgo
dwouldha
vegivenu
sroots

The coded message is obtained by reading down the columns going left to right.

For example, the message above is coded as:

imtgdvs fearwer mayoogo anouuio ntnnlvt wttddes aohghn sseoau

Write a program that, given an English text, outputs the encoded version of that text.

The size of the square (number of columns) should be decided by the length of the message.

If the message is a length that creates a perfect square (e.g. 4, 9, 16, 25, 36, etc), use that number of columns.

If the message doesn't fit neatly into a square, choose the number of columns that corresponds to the smallest square that is larger than the number of characters in the message.

For example, a message 4 characters long should use a 2 x 2 square. A message that is 81 characters long would use a square that is 9 columns wide.

A message between 5 and 8 characters long should use a rectangle 3 characters wide.

Output the encoded text grouped by column.

For example:

• "Have a nice day. Feed the dog & chill out!"
  • Normalizes to: "haveanicedayfeedthedogchillout"
  • Which has length: 30
  • And splits into 5 6-character rows:
    • "havean"
    • "iceday"
    • "feedth"
    • "edogch"
    • "illout"
  • Which yields a ciphertext beginning: "hifei acedl v…"

Getting Started

Make sure you have read the C++ page on exercism.io. This covers the basic information on setting up the development environment expected by the exercises.

Passing the Tests

Get the first test compiling, linking and passing by following the three rules of test-driven development. Create just enough structure by declaring namespaces, functions, classes, etc., to satisfy any compiler errors and get the test to fail. Then write just enough code to get the test to pass. Once you've done that, uncomment the next test by moving the following line past the next test.

#if defined(EXERCISM_RUN_ALL_TESTS)

This may result in compile errors as new constructs may be invoked that you haven't yet declared or defined. Again, fix the compile errors minimally to get a failing test, then change the code minimally to pass the test, refactor your implementation for readability and expressiveness and then go on to the next test.

Try to use standard C++11 facilities in preference to writing your own low-level algorithms or facilities by hand. CppReference is a wiki reference to the C++ language and standard library. If you are new to C++, but have programmed in C, beware of C traps and pitfalls.

Source

J Dalbey's Programming Practice problems view source