A number composed of one or more ASCII digits (ie "0" or "1234") OR
A simple word composed of one or more ASCII letters (ie "a" or "they") OR
A contraction of two simple words joined by a single apostrophe (ie "it's" or "they're")

When counting words you can assume the following rules:

The count is case insensitive (ie "You", "you", and "YOU" are 3 uses of the same word)
The count is unordered; the tests will ignore how words and counts are ordered
Other than the apostrophe in a contraction all forms of punctuation are ignored
The words can be separated by any form of whitespace (ie "\t", "\n", " ")

For example, for the phrase "That's the password: 'PASSWORD 123'!", cried the Special Agent.\nSo I fled. the count would be:

that's: 1
the: 2
password: 2
123: 1
cried: 1
special: 1
agent: 1
so: 1
i: 1
fled: 1

Note that the tests for this exercise expect the output words to be proper C strings. That is, they should be NUL terminated. See https://en.wikipedia.org/wiki/C_string_handling

Getting Started

Make sure you have read the "Guides" section of the C track on the Exercism site. 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.

The included makefile can be used to create and run the tests using the test task.

make test

Create just the functions you need 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, move onto the next test.

As you progress through the tests, take the time to refactor your implementation for readability and expressiveness and then go on to the next test.

Try to use standard C99 facilities in preference to writing your own low-level algorithms or facilities by hand.

Source

This is a classic toy problem, but we were reminded of it by seeing it in the Go Tour.

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.