Replacing NULL with 0 in a SQL server query

I have developed a query, and in the results for the first three columns I get NULL. How can I replace it with 0?

  Select c.rundate, 
    sum(case when c.runstatus="Succeeded" then 1 end) as Succeeded, 
    sum(case when c.runstatus="Failed" then 1 end) as Failed, 
    sum(case when c.runstatus="Cancelled" then 1 end) as Cancelled, 
    count(*) as Totalrun from
    (    Select a.name,case when b.run_status=0 Then 'Failed' when b.run_status=1 Then 'Succeeded'
    when b.run_status=2 Then 'Retry' Else 'Cancelled' End as Runstatus,
    ---cast(run_date as datetime)
                cast(substring(convert(varchar(8),run_date),1,4)+"https://stackoverflow.com/"+substring(convert(varchar(8),run_date),5,2)+"https://stackoverflow.com/"          +substring(convert(varchar(8),run_date),7,2) as Datetime) as RunDate
    from msdb.dbo.sysjobs as a(nolock) inner join msdb.dbo.sysjobhistory as b(nolock) 
    on a.job_id=b.job_id
    where a.name="AI"
    and b.step_id=0) as c
    group by 
    c.rundate