Create sharepoint custom group and assign pemissions

Get all the Sub Sites and bind to drop down list

void BindSite(SPSite mySite)
    {
     
        SPWebCollection subSites = mySite.AllWebs;
        foreach (SPWeb site in subSites)
        {
            ddlSourceSite.Items.Add(site.Url);

        }
    }

Create a Group under a sub site and assign permission to Created Group

 string strGrpName = drpGrpName.SelectedItem.Text.Trim();
        string strpermission = DropDownList1.SelectedItem.Text.Trim();
        using (SPSite curSite = new SPSite(ddlSourceSite.SelectedItem.Value))
        {
            using (SPWeb oweb = curSite.OpenWeb())
            {
                if (!isGrpExists(oweb, strGrpName))
                {
                    SPUser user = oweb.CurrentUser;
                    oweb.AllowUnsafeUpdates = true;
                    oweb.SiteGroups.Add(strGrpName, user, user, txtGrpDescr.Text.Trim());
                    SPGroup group = oweb.SiteGroups[strGrpName];

                    SPRoleAssignment asgn = new SPRoleAssignment(oweb.SiteGroups[strGrpName]);
                    SPRoleDefinition con = oweb.RoleDefinitions[strpermission];
                    asgn.RoleDefinitionBindings.Add(con);

                    oweb.RoleAssignments.Add(asgn);

                    oweb.AssociatedGroups.Add(group);
                    oweb.Update();




                }
                else
                {
                    Response.Write("Group Already Existed");
                }
            }
        }
///Check the group is existed or not..in current web
bool isGrpExists(SPWeb oweb, string strGrpName)
    {
        try
        {
            SPGroup group1 = oweb.Groups[strGrpName];
            return true;
        }
        catch (Exception ex)
        {
            return false;
        }
    }