Short answers, pulled from the story.
A Clockwork Orange was withdrawn from British cinemas in 1973 at the request of director Stanley Kubrick, after the film was linked by prosecutors and the press to real acts of violence, including the manslaughter of a schoolboy and the murder of an elderly vagrant in Bletchley, Buckinghamshire. The ban remained in effect until Kubrick died in 1999, making the film unavailable in UK cinemas for approximately 27 years.
Malcolm McDowell plays Alex DeLarge. Kubrick cast him after seeing him in the 1968 film if..., telling McDowell: "You can exude intelligence on the screen." McDowell also contributed to the production by showing Kubrick the cricket whites he owned, which became part of Alex's gang uniform.
The Ludovico Technique is the film's experimental aversion therapy, promoted by the Minister of the Interior. Alex is strapped to a chair with his eyes clamped open, injected with drugs, and forced to watch films of sex and violence. The technique is widely interpreted as a parody of classical conditioning, and the film's prison chaplain argues it robs Alex of his free will.
"Singin' in the Rain" was an improvisation by Malcolm McDowell on the fifth day of filming the rape scene, after Kubrick asked him if he could dance. McDowell chose it because it was the only song he "sort of knew half the lyrics to." The song does not appear in Burgess's novel.
Kubrick based his screenplay on the American edition of the novel, which omitted the final chapter in which Alex matures and outgrows his sociopathy. The film therefore ends with Alex being offered a government job while still a sociopath, whereas the complete novel ends with his genuine reform. Kubrick said he never seriously considered using the omitted chapter, finding it unconvincing.
A Clockwork Orange grossed $41 million in the United States and approximately $73 million overseas, for a worldwide total of $114 million against a production budget of $1.3 million. It was the most popular film of 1972 in France with 7,611,745 admissions, and played for over a year at the Warner West End cinema in London.