Problem for using Asp.net c# and html mixing code

I tried to use below code in asp.net but there is error in html tags like and and say it could not find begin tag. but begin tag is in first if. the errors are in between line 44 to 52.

@{string n ="";int j =0;foreach(var item inModel.RelatedProduct){if(item.ProductId!= n)
                j =1;else
                j =0;if(j==1){<div class="modal fade" id="myModal" role="dialog"><div class="modal-dialog modal-dialog-centered " role="document"><div class="modal-content"><div class="modal-header"><h5 class="modal-title">@item.CatalogDescription</h5><button class="close" type="button" data-dismiss="modal"><span aria-hidden="true">&times;</span></button></div><div class="modal-body"><table class="table table-hover"><thead class="thead-dark"><tr><td>Customer</td></tr>}@if(j ==1|| j ==0){<tr><td>@item.CustomerName</td><td>@item.Price</td></tr>}@if(j==1){</table></div><div class="modal-footer"><button class="btn" data-dismiss="modal">Cancel</button></div></div></div></div>}}}