The pronoun hic (this) is written with short i in many places, e.g. Oxford Latin Dictionary. But in Lewis & Short: Latin-English dictionary and Allen and Greenough's New Latin Grammar, it is written as hīc with a long i.
Which is correct?
The vowel in the pronoun hic is certainly short, but in poetry the word often (not always!) scans as long even when it is followed by a vowel, as if it were actually hicc. This is not etymologically defensible, but it happens in analogy with the neuter nom./acc. sg. hо̆c (which L&S also has as hōc despite its short vowel), which is always hocc when followed by a vowel (in pronunciation and scansion if not in actual writing), because it reflects an older pronoun *hod + the deictic particle -c(e) (also seen in e.g. illic (ille + -c), tunc (tum + -c)), with assimilation of the d to the c.
The resulting geminate consonant disappears phonotactically when followed by a consonant or hiatus, which is presumably why it isn't written, but it's still lurking underneath. hic reflects *hĭ + the same particle and so doesn't genuinely/originally have the geminate, but it does show up.
L&S, like a lot of older works, uses macrons to indicate syllable weight, not vowel length. It's often the same thing, but not in this case.
(The adverb hīc does have a genuine long vowel, and so do some of the (other) declined forms of the pronoun.)