Objective-C, used for developing Apple iOS applications, climbs to Number 6 in the monthly Tiobe Programming Community index for most popular programming languages, after being ranked at number 8 a year ago. Also posting gains, C# rose to No. 4, a jump of two spots a year ago, while PHP dropped from Number 4 at this time last year to Number 5.

D, meanwhile, had been in the top 20 from 2007 until the middle of 2009 and was ranked 20 in the September report. Tiobe points to a Wikipedia reference about the release of a book entitled "The D Programming Language," by Andrei Alexandrescuin June 2010, as a possible reason for the language's comeback.

The D language is from Digital Mars and can be viewed as somewhat of a successor to C++, although C++ is still popular, said Paul Jansen, founder and chief community officer of Tiobe, which assesses software quality: "D is in fact a clean design of C++."

The rising popularity of D and F#

D displaces the F# language, which briefly cracked the Tiobe top 20 last month. F#, a functional language for Microsoft's .Net platform, was ranked No. 20 in August, its first-ever entrance in the top 20. But it dropped to the 23rd-most popular language in the September report.

But F#, representing a new generation of functional languages, can be expected to quickly return to the top 20, Jansen said: "It's a functional language, which means that it is a completely different way of programming. There have been a lot of functional languages around so far, and the most famous one is Lisp."

Java's still Number One

Java remains No. 1 on the Tiobe list, followed by C, C++, C#, and PHP. Between Objective-C and D, the top 20 was filled out by Visual Basic, Python, Perl, JavaScript, Ruby, Delphi/Object Pascal, Lua, Lisp, Transact-SQL, Pascal, PL-SQL, Ada, and RPG (OS/400). Java has been the top language for 10 years, except for a few months when it was eclipsed by C, Jansen said.

Tiobe Software's index gauges the popularity of languages based on an assessment of search engine page views pertaining to the languages. Search engines such as Google, Bing and Yahoo are used to calculate ratings, along with other popular sites for software development, such as Wikipedia, Baidu and even YouTube.