C [L1 ] is a programming language found first [L2 ] on Unix systems but now found on many platforms. The Tcl and Tk core is written in C.
C FAQ: http://c-faq.com/
The ANSI committee as well as the ISO committee have approved a standard reference for C (as well as I believe a few revisions).
See http://www.lysator.liu.se/c/ for pointers to various papers. [L3 ] (big HTML file) seems to be a newer version of the C99 standard than lysator provides.
Support for C is traditionally provided by a compiler.
The FSF's gcc compiler is a quite popular C compiler found on many platforms and operating systems.
Also, most Unix systems have vendor supported compilers. They are often unbundled products these days. Sun is one of the vendors who have this type of product.
There is also tcc, the "Tiny C Compiler".
[In the following list, be certain to indicate whether or not you have built Tcl and Tk with the compiler in question.] On Microsoft Windows there are many options, including
etc.
The number of C compilers available on MacOS is more limited. There is
Support for C can also take the form of an interpreter.
For instance, a recent advertisement for Ch, a product at http://www.softintegration.com/ , is interesting. It is a C/C++ interpreter that runs cross-platform on a large number of operating systems and hardware. It provides not only standard language features, but also support for 2 and 3 dimensional plotting, shell programming, and numerical programming. It supports 1990 ISO C standard as well as C99 features. In Jan, 2003, the product page for Ch Standard says that the product is free for use on Unix, Linux, and Mac OS X.
See also EiC [L13 ], another C interpreter.
See as well CInt (free) from Masaharu Goto originally apparently maintenance was taken over by the CERN Root team which uses CInt as its scripting language (http://root.cern.ch/root/Cint.html ) I do not know if Tcl can be interpreted under this interpreter RFox.
Support for C can also take the form of a run-time compiler.
tcc provides a libtcc library, which allows a running program to compile and link C code without touching disk. In milliseconds for a small chunk of code. (x86 only as of Jun 2003) - see also Odyce.
AMG: One annoying thing about C is that, like Fortran, it uses "=" as its assignment operator. This is very easy to confuse with the comparison operator "==", resulting in either of the following two coding errors:
x == 5; /* Nothing happens, except maybe a warning if -Wall is on. */ if (x = 6) {...} /* Unintended assignment and incorrect logic. */
Algol uses ":=" as its assignment operator, and C is ancestrally derived from Algol, so I was always mystified about why C reverted to Fortran's assignment syntax. But I just now figured it out, I think. A ":=" assignment operator looks almost identical to C's "!=" inequality operator, so using ":=" instead of "=" for assignment simply trades one potential coding error for another. To fix that problem, "!=" would have to be replaced with, say, "/=" (borrowed from Ada), but that (1) collides with the compound division and assignment operator "/=" and (2) breaks symmetry with the logical negation operator "!". Or instead use "\=", but that will behave unexpectedly when placed inside double quotes. Or use "<>" and be like BASIC and SQL. Shrug!