error occured

Question

string StrQuery;
try
{
using (SqlConnection conn = new SqlConnection(ConnString))
{
using (SqlCommand comm = new SqlCommand())
{
comm.Connection = conn;
conn.Open();
for(int i=0; i< dataGridView1.Rows.Count;i++)
{
StrQuery= @"INSERT INTO tableName VALUES ("
+ dataGridView1.Rows[i].Cells["ColumnName"].Value +", "
+ dataGridView1.Rows[i].Cells["ColumnName"].Value +");";
comm.CommandText = StrQuery;
comm.ExecuteNonQuery();
}
}
}

i written the code like this.but i got error,use of un assigned local variable 'StrQuery'