While the output from your program may be encoding the plaintext, the problem lies elsewhere. The program spec says to prompt for input. The code above merely waits for input, without a prompt. Perhaps a review of the program spec is in order? There is specific instruction about the prompt and what follows.
One of the hidden lessons in the early psets is that the programs must be written to conform to exactly what is required in the spec. This is especially important in team programming environments when different programmers work on different functions that must later function together.
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