SQL Server :: Add Only Homework1(h1) For Specific Student Number - Convert Null Values To Integer?

i have atable:

STDNo nvarchar(6) //student number primary
CID nvarchar(7) //course ID primary
DNo int //Department Number primary
H1 int allow null // Home work 1
H2 int allow null
H3 int allow null
H4 int allow null
H5 int allow null
Q1 int allow null //Quize 1
Q2 int allow null
Q3 int allow null
Q4 int allow null
Q5 int allow null
HE1 int allow null
HE2 int allow null
FExam int allow null // Final Exam

and stored procedure like this:

ALTER procedure [dbo].[AddMonthlyMarks]
(
@STDNo nvarchar(6),
@CID nvarchar(7),
@Dno int =isnull,
@H1 int,
@H2 int,..........................

the Data key name of grid is STDNo the problem is that the instructor this month will add only homework1(h1) for specific student number or to all students and rest of home works and quezies will not entered (Null), to the next month he will enter home work 2 ,etc... i get an error and i think that the null values for others home works in grid make this error caution: in table i check allow null property,the data type is integer How i can convert this null values to integer?