帮看一条SQL语句，错哪了_Sql Server

帮看一条SQL语句，哪里错了
string strupdate = "insert into table16 (title,username,time,content,class) values (" + TextBox1.Text.ToString() + " , " + "' 1 '" + " ,"+ DateTime.Now+ ", " + TextBox4.Text.ToString() + " , " + "'1'" + " )";
就是上面这句，求指教

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C# code

--字符串都要加单引号引起来的string strupdate = "insert into table16 (title,username,time,content,class) values ('" + TextBox1.Text.ToString() + "' , " + "' 1 '" + " ,'"+ DateTime.Now+ "', '" + TextBox4.Text.ToString() + "' , " + "'1'" + " )";
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试试把DateTime.Now改为DateTime.Now.ToString()
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拼出来的句子 字符串和日期要有单引号,你的没有