I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W). My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.

There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.

• ACM Turing Award for "fundamental contributions to the definition and design of programming languages". The award was presented to him at the ACM Annual Conference in Nashville, Tennessee, on 27 October 1980, by Walter Carlson, Chairman of the Awards committee. A transcript of Hoare's speech was published in Communications of the ACM.
• Harry H. Goode Memorial Award (1981)
• Fellow of the Royal Society (1982)
• Honorary Doctorate of Science by the Queen's University Belfast (1987)
• Knighted for services to education and computer science (2000)
• Kyoto Prize for Information science (2000)
• Fellow of the Royal Academy of Engineering (2005)
• Computer History Museum (CHM) in Mountain View, California Fellow of the Museum "for development of the Quicksort algorithm and for lifelong contributions to the theory of programming languages" (2006)
• Honorary Doctorate of Science from the Department of Informatics of the Athens University of Economics and Business (AUEB) (2007)