<%= @user.post.size%>

<% size = @user.post.size %>
<%= (size == 0) ? nil : size %>

<% size = @post.comments.size %>
<%= (size == 0) ? nil : size %>

# Set the variable in
<% size = @user.post.size %>

# Display size unless it is zero.
<%= size unless size.zero? %>

@post.comments.any?
@user.post.size.nil?