关于赋值，这个错误怎么改？

Question

protected void Page_Load(object sender, EventArgs e) 
    {         if (!this.Page.IsPostBack) 
        { 
          string v7; 
            SqlCommand cmd = new SqlCommand(); 
            
            SqlConnection con = new SqlConnection("Server=(local);user id=sa;pwd=;database=master"); 
            con.Open(); 
            SqlDataAdapter ap = new SqlDataAdapter("select sum(expend) from account_bill",con); 
            v7 = ap; 
            this.label.Text =v7; 
            con.Close();         } 
提示错误： 错误 1 无法将类型“System.Data.SqlClient.SqlDataAdapter”隐式转换为“string” 

Answer 1

string v7;
            SqlCommand cmd = new SqlCommand();            SqlConnection con = new SqlConnection("Server=(local);user id=sa;pwd=;database=master");
            con.Open();
            SqlDataAdapter ap = new SqlDataAdapter("select sum(expend) from account_bill", con);
            DataTable dt = new DataTable();
            ap.Fill(dt);
            if (dt != null && dt.Rows.Count > 0)
            {
                v7 = dt.Rows[0][0].ToString();
            }
            con.Close();

Answer 2

[code=BatchFile]string sql="select sum(expend) from account_bill;
SqlCommand cmd = new SqlCommand(sql, con);
con.Open(); 
string v7 = cmd.ExecuteScalar();
this.label.Text =v7; 
con.Close[/code]
楼主有点复杂化问题了

Answer 3

string v7; 
            SqlCommand cmd = new SqlCommand(); 
            
            SqlConnection con = new SqlConnection("Server=(local);user id=sa;pwd=;database=master"); 
            con.Open(); 
            SqlDataAdapter ap = new SqlDataAdapter("select sum(expend) from account_bill",con); 
            v7 = ap; 
            this.label.Text =v7; 
            con.Close(); 
这也能赋值？找基础的书看看先吧

Answer 4

改好了，但是有一个错误：protected void Page_Load(object sender, EventArgs e)
    {        if (!this.Page.IsPostBack)
        {
            SqlConnection con = new SqlConnection("Server=(local);user id=sa;pwd=;database=master");
            string sql="select sum(expend) from account_bill";
            SqlCommand cmd = new SqlCommand(sql,con);
            con.Open();
            string v7 = cmd.ExecuteScalar();
            this.label.Text = v7;
            con.Close();        }
    }错误 1 无法将类型“object”隐式转换为“string”

Answer 5

非常感谢shadowjl ！感谢各位！

Answer 6

楼主多看看书，顺便结贴。protected void Page_Load(object sender, EventArgs e) 
    {         if (!this.Page.IsPostBack) 
        { 
          string v7; 
            SqlCommand cmd = new SqlCommand(); 
            
            SqlConnection con = new SqlConnection("Server=(local);user id=sa;pwd=;database=master"); 
            con.Open(); 
            cmd.CommandText="select sum(expend) from account_bill";
            cmd.Connection=con;
                         v7 = cmd.ExecuteScalar().ToString(); 
            this.label.Text =v7; 
            con.Close();         }