Algerian President Chadli Bendjedid declared a state of emergency Thursday on the second day of widespread rioting against his government's economic policies, and witnesses said troops fired on the demonstrators. A column of Algerian army tanks moved on the capital of Algiers from the city of Blida, 30 miles to the south, sources said. Soldiers in combat gear with fixed bayonets on their rifles guarded the Parliament building and key government offices. The rioting erupted for a second day Thursday.