I am trying to get my submit button for to be on a different page but I get this error. I have the following in my show.html.erb,

<div class="post-page">
    <div class="panel panel-default">
        <div class="panel-heading-gray">
            <%= @user.name %> | <button type="button" class="btn btn-primary" data-toggle="modal" data-target="#exampleModal" data-whatever="@mdo">Edit<%= link_to edit_post_path(@post) %></button> | <%= link_to 'Delete', post_path, method: :delete, data: { Confirm: "Are you sure?" } %><i class="fa fa-times"></i> </div>
        <div class="panel-body"><h3><%= @post.body %></h3></div>
           <div class="panel-footer">
            Posted <%= time_ago_in_words(@post.created_at) %> Ago
           </div>
</div>

  <div class="modal fade" id="exampleModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
<div class="modal-dialog">
  <div class="modal-content">
    <div class="modal-header">
      <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">×</span></button>
          <h4 class="modal-title" id="exampleModalLabel">Edit Post</h4>
        </div>
        <div class="modal-body">
         <form>
            <div class="form-group">
               <label for="message-text" class="control-label">Message:</label>
              <%= render 'form' %>
            </div>
      </form>
        </div>
        <div class="modal-footer">
          <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
          <%= f.submit %>
        </div>
      </div>
    </div>
  </div>

</div>

This is in my _form.html.erb page,

 <% form_for @post do |f| %>
    <% if @post.errors.any? %>
      <div id="errors">
        <h2><%= pluralize(@post.errors.count, "Error") %> Prevent this post from posting</h2>
        <ul>
            <% @post.errors.full_messages.each do |msg| %>
            <li><%= msg %></li>

            <% end %>
        </ul>
      </div>
    <% end %>
    <p>
         <%= f.label :body %><br>
         <%= f.text_area :body %>
    </p>
    <p>
        <%= f.submit %>
    </p>
<% end %>

This is in my posts_controller.rb,

class PostsController < ApplicationController
def index
    @posts = Post.all.order("created_at DESC")
end
def welcome
    @user = User.find(session[:user_id])
    @post = Post.find(params[:id])
    @posts = Post.order("created_at desc").limit(4).offset(1)
    @signed_in_user = session[:user_id]
end
def new
    @post = Post.new
end
def create
    @post = Post.new(post_params)

    @post.user_id = @signed_in_user

if  @post.save
    redirect_to dashboard_path
else
    render 'new'
end
end
def show
    @user = User.find(session[:user_id])
    @post = Post.find(params[:id])
    @posts = Post.order("created_at desc").limit(4).offset(1)
    @signed_in_user = session[:user_id]

end
def edit
    @post = Post.find(params[:id])
end

def update
    @post = Post.find(params[:id])

    if @post.update(params[:post].permit(:body))
        redirect_to @post
    else
        render 'edit'
    end
end
def destroy
    @post = Post.find(params[:id])
    @post.user_id = @signed_in_user

    @post.destroy

    redirect_to posts_path
end

private
def post_params
    params.require(:post).permit(:body)
end
end

I have even tried rendering partials thinking that maybe it could help, I have tried several things overall but can't seem to figure this out. I am sure its very simple and I am missing it but if you know how to fix it then post your answer and thank you in advance! I can also add any other code you may need to see that can help this process!

f is only available in the form_for block, which is being prematurely closed with the first <% end %>.

<% form_for @post do |f| %>
      </div>
    <% end %> <!-- Closes form_for; remove this line  -->
    <p>
         <%= f.label :body %><br>
         <%= f.text_area :body %>
    </p>
    <p>
        <%= f.submit %>
    </p>
<% end %>

Edit:

<button type="button" class="btn btn-primary"><%= f.submit %></button> in show.html.erb is also outside of the context of the form block. Move this line to _form.html.erb, before the closing <% end %> and your error should disappear.

This will solve the error, but your form will not be output unless you modify the opening tag as Eifion suggested.