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Project: a secret code

Encode the message with the shift: letters move forward, spaces stay as they are. hello world with a shift of 3 should print khoor zruog.

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A shift code (a Caesar cipher) swaps every letter for the one a few places along the alphabet, so with a shift of 3, a becomes d and z wraps round to c. In Python ord("a") gives a letter's number (97) and chr(97) turns a number back into a letter. Subtract 97 to count letters from 0, add the shift, use % 26 to wrap, then add 97 back.

Your task

Encode the message with the shift: letters move forward, spaces stay as they are. hello world with a shift of 3 should print khoor zruog.

Stretch challenge

Add a second code that only changes vowels. Can your friend crack it?

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Project: the snack bill

Print three lines: Subtotal: 270, Tax: 13.5, Total: 283.5, worked out from the three prices.

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Project: break the code

Write decode(text, shift) that undoes a shift code, and use it to read wkh txlfn eurzq ira (shift 3).

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