Why encoding is required in week1 in notation

why one-hot encoding is required for the words in sentence ?
For each word we have a separate one-hot encoding vector and if suppose we have 20 words in sentence or 100 words in sentence is it feasible to have a vector for each word ?

One-hot coding identifies a word within the vocabulary.
If you have 100 words in a sentence, then the sentence is represented by 100 vectors.

is it feasible to use 100 vectors or do we have any other way ?