I am facing one problem while adding alert programmatically.

I want to send alert email to multiple users but not able to
know how to do that programmatically.

I am writing like that way :
SPAlert alert;

alert.Properties["dynamicrecipient"]
= "<Query><And><And><Eq><FieldRef
Name=\"AssignedTo\"/><Value type=\"string\">" + "nishm_2000@..." +
"</Value></Eq><Neq><FieldRef
Name=\"Status\"/><Value
type=\"string\">completed</Value></Neq></And><Leq><FieldRef
Name=\"StartDate\"/><Value
type=\"datetime\"><Today/></Value></Leq></And></Query>";

also tried this way :

alert.DynamicRecipient = "<Query><And><And><Eq><FieldRef
Name=\"AssignedTo\"/><Value type=\"string\">" + " nishm_2000@..." +
"</Value></Eq><Neq><FieldRef
Name=\"Status\"/><Value
type=\"string\">completed</Value></Neq></And><Leq><FieldRef
Name=\"StartDate\"/><Value
type=\"datetime\"><Today/></Value></Leq></And></Query>";