def camel_to_c(word):
    """
    Convert camel case to c case.

    Args:
        word: A string.

    Returns:
        A c case string.
    """
    n_word = word[0]

    for chara in word[1:]:
        if chara.isupper():
            n_word += '_'

        n_word += chara

    return n_word.lower()