show.html.erb

<h2><%= @post.title %></h2>
<p><%= @post.body %></p>

<hr>
<%= link_to "Edit", edit_post_path(@post), :class => 'btn btn-default' %>
<%= link_to "Delete", post_path(@post), method: :delete,
    data: {confirm: 'Are you sure?'},
    :class => 'btn btn-danger' %>

<hr>
<h3>Comments</h3>
<% @post.comments.each do |comment| %>
    <div class="well">
        <p><strong><%= comment.username %></strong>: <%= comment.body %></p>
    </div>
<% end %>

<h3>Add Comment</h3>
<%= form_for([@post, @post.comments.build]) do |f| %>
    <p>
        <%= f.label :username %><br>
        <%= f.text_field :username, class: 'form-control' %>
    </p>

    <p>
        <%= f.label :body %><br>
        <%= f.text_field :body, class: "form-control" %>
    </p>

    <p>
        <%= f.submit class: 'form-control' %>
    </p>
<% end %>