How can i update DataGrid view value from another form textbox value

Dear Sachin, 

Thank you for your reply.

But issue you can see below snap when i double click the griview row data is coming from same row in another form textbox but when i am updating showing error like below.

 

Error

create a class file in your project as

 public class Class1 {  
    static string _grampcs, _unitprice,_total;  
    public static string grampcs{  
      get {  
        return _grampcs;  
      }  
      set {  
        _grampcs= value;  
      }  
    }  
    public static string unitprice{  
      get {  
        return _unitprice;  
  
      }  
      set {  
        _unitprice= value;  
      }  
    }  

    public static string total{  
      get {  
        return _total;  
  
      }  
      set {  
        _total= value;  
      }  
    }  
  }  

In Form 2 (where you have textboxes) set the above fields as

Class1.total=txtTotal.Text;
//so on for other fields

in First form (Where you have DataGridView)

Main_dg.Rows[i].Cells[2].Value = Class1.txtupdate_grampcs;
            Main_dg.Rows[i].Cells[3].Value = Class1.unitprice;
            Main_dg.Rows[i].Cells[4].Value = Class1.total;