Yes, I used THINK/Lightspeed C for several projects in the late 1980s. It was great: a good editor, a decent compiler, and good documentation. It was an interesting hybrid between 'traditional' C and object-oriented languages like Smalltalk. As I recall, its object system was simplistic, mostly about class inheritance & instance construction — but then again, I was young and inexperienced. But I did realize a few years later, when I got into early Java and C++ and Objective-C, how graceful the THINK C object system was, without a lot of weird cruft like operator overloading or generics.
I never knew of the "Atari Lightspeed C" until just now! These two you mention were entirely unrelated, AFAIK. I know this because I worked at THINK on LightspeedC with Michael Kahl. He was the sole author of the compiler and UI system (with the possible exception of the text editor, written by Jon Hueras). I wrote the standard C libraries and the initial draft of the user manual (since there was no one else to do it!). Later renamed ThinkC because of a conflict with Lightspeed company/corporation in Boston (who I think did typesetting) who complained to us that too many people were calling them about LightspeedC and they did not appreciate it (and they make have threatened a trademark dispute?). The C++ standard was not yet solidified, so the first version to incorporate the C++ draft standard was simply called "ThinkC with Objects" and Greg Dow wrote a series of app classes that made everything very competitive as an alternative to the MacApp framework (which I never liked!). I used ThinkC and those app classes to create a video title product called "Bola32" for Flamingo Graphics of Cambridge, MA. Also subsequently used ThinkC (in the early 1990s) for a very large application known as the "Avid Media Composer" which is a video editor. The BIG DEAL with LightspeedC was that it was loosely modeled after Borland's TurboC and the idea was for very fast turnaround coding/testing cycles. You would simply code C programs then run them. And it did that VERY FAST, using advanced techniques as incremental linking (none of that MAKE business!). THINK had previously created Macintosh Pascal, which, unlike LightspeedC, was a fully interpreted language, to Apple computer for the early Macintosh.
Yes, I used THINK/Lightspeed C for several projects in the late 1980s. It was great: a good editor, a decent compiler, and good documentation. It was an interesting hybrid between 'traditional' C and object-oriented languages like Smalltalk. As I recall, its object system was simplistic, mostly about class inheritance & instance construction — but then again, I was young and inexperienced. But I did realize a few years later, when I got into early Java and C++ and Objective-C, how graceful the THINK C object system was, without a lot of weird cruft like operator overloading or generics.
I never knew of the "Atari Lightspeed C" until just now! These two you mention were entirely unrelated, AFAIK. I know this because I worked at THINK on LightspeedC with Michael Kahl. He was the sole author of the compiler and UI system (with the possible exception of the text editor, written by Jon Hueras). I wrote the standard C libraries and the initial draft of the user manual (since there was no one else to do it!). Later renamed ThinkC because of a conflict with Lightspeed company/corporation in Boston (who I think did typesetting) who complained to us that too many people were calling them about LightspeedC and they did not appreciate it (and they make have threatened a trademark dispute?). The C++ standard was not yet solidified, so the first version to incorporate the C++ draft standard was simply called "ThinkC with Objects" and Greg Dow wrote a series of app classes that made everything very competitive as an alternative to the MacApp framework (which I never liked!). I used ThinkC and those app classes to create a video title product called "Bola32" for Flamingo Graphics of Cambridge, MA. Also subsequently used ThinkC (in the early 1990s) for a very large application known as the "Avid Media Composer" which is a video editor. The BIG DEAL with LightspeedC was that it was loosely modeled after Borland's TurboC and the idea was for very fast turnaround coding/testing cycles. You would simply code C programs then run them. And it did that VERY FAST, using advanced techniques as incremental linking (none of that MAKE business!). THINK had previously created Macintosh Pascal, which, unlike LightspeedC, was a fully interpreted language, to Apple computer for the early Macintosh.
Used Think Pascal in college. Great IDE and manuals. Then Codewarrior came along.