Assign Permission to sharepoint groups programmatically

In this post I am showing you how to assign custom permissions to sharepoint groups.

Add following namespaces:
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using Microsoft.SharePoint;
using System.Resources;
using System.Reflection;
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namespace Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            SPSite site = new SPSite("URL");
            SPWeb web = site.OpenWeb();
            ResourceManager rm = new ResourceManager("DemoFolder.Resource1", Assembly.GetExecutingAssembly());     //We are creating resource file and taking info from there.
            string MUFolder = rm.GetString("MUFolder");
            string[] grpmu = MUFolder.Split(',');
            string CntryFolder = rm.GetString("CntryFolder");
            string[] grpCntry = CntryFolder.Split(',');
            string CCfolder = rm.GetString("CCfolder");
            string[] grpcc = CCfolder.Split(',');
            string fold = rm.GetString("Folder");
            string[] grpList = fold.Split(',');

          for (int i = 0; i < grpList.Length; i++)
            {
                SPList list = web.Lists["CustomList"];
                SPQuery query = new SPQuery();
                query.Query = "<Where><Eq><FieldRef Name='Title'/><Value Type='Text'>" + grpList[i] + "</Value></Eq></Where>";
                SPListItemCollection items = list.GetItems(query);
                foreach (SPListItem item in items)
                {
                    SPFolder folder = web.GetFolder(item.Url);
                    folder.Item.BreakRoleInheritance(true);
                    SPGroupCollection spc = web.SiteGroups;
                    foreach (SPGroup oGroup in spc)
                    {
                        folder.Item.RoleAssignments.Remove((SPPrincipal)oGroup);
                    }
                    Console.WriteLine("All existing groups are removed");
                    SPRoleAssignment roleAssignment = new SPRoleAssignment((SPPrincipal)web.SiteGroups[grpmu[i]]);
                    roleAssignment.RoleDefinitionBindings.Add(web.RoleDefinitions["Country"]);
                    folder.Item.RoleAssignments.Add(roleAssignment);
                    Console.WriteLine("Assigned " + grpmu[i] + " to " + grpList[i]);
                    SPRoleAssignment roleAssignment1 = new SPRoleAssignment((SPPrincipal)web.SiteGroups[grpcc[i]]);
                    roleAssignment1.RoleDefinitionBindings.Add(web.RoleDefinitions["Country"]);
                    folder.Item.RoleAssignments.Add(roleAssignment1);
                    Console.WriteLine("Assigned " + grpcc[i] + " to " + grpList[i]);
                    SPRoleAssignment roleAssignment2 = new SPRoleAssignment((SPPrincipal)web.SiteGroups[grpCntry[i]]);
                    roleAssignment2.RoleDefinitionBindings.Add(web.RoleDefinitions["Country"]);
                    folder.Item.RoleAssignments.Add(roleAssignment2);
                    Console.WriteLine("Assigned " + grpCntry[i] + " to " + grpList[i]);
                    SPRoleAssignment roleAssignment3 = new SPRoleAssignment((SPPrincipal)web.SiteGroups["Custom"]);
                    roleAssignment3.RoleDefinitionBindings.Add(web.RoleDefinitions["Custom"]);
                    folder.Item.RoleAssignments.Add(roleAssignment3);
                    Console.WriteLine("Assigned Custom to " + grpList[i]);
                    SPRoleAssignment roleAssignment4 = new SPRoleAssignment((SPPrincipal)web.SiteGroups["ReadOnlyUser"]);
                    roleAssignment4.RoleDefinitionBindings.Add(web.RoleDefinitions["ReadOnlyUser"]);
                    folder.Item.RoleAssignments.Add(roleAssignment4);
                    Console.WriteLine("Assigned ReadOnlyUser to " + grpList[i]);
                    web.Update();
                }
            }
            site.Dispose();
}
}
}
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This way we can assign permissions programmatically.