Error - Cannot perform '=' operation on System.Int32 and System.String.

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C#

Why the error is comming after running this program in localhost.

Error - Cannot perform '=' operation on System.Int32 and System.String.


My cs program is given below

void del(Object Sender, EventArgs e)
{
string agent = Request.QueryString["CODNO"];
string sa=txtACode.Text.Trim();
int r=0;
con.Open();
DataRow []rs;
rs=ds.Tables["joining"].Select("agent='" + sa + "'");
//rs=ds.Tables["joining"].Select("agent='" + sa + "'");
r=rs.Length;
if (txtACode.Text=="")
{
com=con.CreateCommand();
com.CommandText="delete * from joining where agent='" + agent + "'";
}
else
{
if(r==0)
{
System.Web.UI.WebControls.Label lbl1=new System.Web.UI.WebControls.Label();
lbl1.ForeColor=System.Drawing.Color.Blue;
lbl1.BackColor=System.Drawing.Color.Yellow;
lbl1.Text="Please enter a velid cerification number to DELETE";
ph1.Controls.Add(lbl1);
}
else if(r>0)
{
DataRow dr;
dr=rs[0];
com=con.CreateCommand();
com.CommandText="delete * from joining where agent='" + sa + "'";
}
else
{
System.Web.UI.WebControls.Label lbl1=new System.Web.UI.WebControls.Label();
lbl1.ForeColor=System.Drawing.Color.Blue;
lbl1.BackColor=System.Drawing.Color.Yellow;
lbl1.Text="No Such Record Found";
ph1.Controls.Add(lbl1);
}
}
try
{
com.ExecuteNonQuery();
System.Web.UI.WebControls.Label lbl1=new System.Web.UI.WebControls.Label();
lbl1.ForeColor=System.Drawing.Color.Blue;
lbl1.BackColor=System.Drawing.Color.Yellow;
lbl1.Text="Record DELETED";
ph1.Controls.Add(lbl1);
}
catch(Exception ex)
{
}
con.Close();
}