Why do you need to do it this way only? As you are already passing Item, Quantity, Price and Date you can do that in a single query. For example:
"delete from Item where Item='" + TextBox1.Text + "' and Quantity='" + TextBox2.Text + "' and Price='" + TextBox3.Text + "' and Date='" + TextBox4.Text + "'" +" and Quantity = 0";
Also, I am not sure this is going to work as you are comparing date which at times can be quite tricky to deal with. And, if you want it in your way only try this:
string po = "0";
string j = "select Quantity from Item";
SqlCommand vvn = new SqlCommand(j, DbConnection.mCon);
SqlDataAdapter lk = new SqlDataAdapter(vvn);
DataTable ui = new DataTable();
lk.Fill(ui);
for(int i = 0; i < ui.Rows.Count; i++)
{
if (ui.Rows[i][0].ToString().Trim()==po)
{
string d6 = "delete from Item where Item='" + TextBox1.Text + "' and Quantity='" + TextBox2.Text + "' and Price='" + TextBox3.Text + "' and Date='" + TextBox4.Text + "'";
SqlCommand cnm6 = new SqlCommand(d6, DbConnection.mCon);
cnm6.ExecuteNonQuery();
}
}
This might not work also as suppose the quantity of first record is "0" but the item,price and Date does not match the passed parameters. You will have to do it the "other" way. Think of it and share with us. We will definitely help you out.