A conforming standard library file math.h is not only not required to, but actually must not define M_PI by default. In this context ‘by default’ means that M_PI must only get defined through compiler-specific tricks, most often undefined behavior through the use of reserved identifiers. Just define the constant yourself (you can use the name … Read more
MSVC is not a C99 compiler, and does not support variable length arrays. At https://learn.microsoft.com/en-us/cpp/c-language/ansi-conformance MSVC is documented as conforming to C90.
In practice, you want some arbitrary precision arithmetic (a.k.a. bigint or bignum) library. My recommendation is GMPlib but there are other ones. Don’t try to code your own bignum library. Efficient & clever algorithms exist, but they are unintuitive and difficult to grasp (you can find entire books devoted to that question). In addition, existing … Read more
char is always a byte , but it’s not always an octet. A byte is the smallest addressable unit of memory (in most definitions), an octet is 8-bit unit of memory. That is, sizeof(char) is always 1 for all implementations, but CHAR_BIT macro in limits.h defines the size of a byte for a platform and … Read more
This is compiler dependent, I’m supposing you’re using GCC. You could check your compiler defined macros using: gcc -dM -E – < /dev/null Check the manual about the flags, specially: ###__STDC_VERSION__### This macro expands to the C Standard’s version number, a long integer constant of the form yyyymmL where yyyy and mm are the year … Read more
int is a “most efficient type” in speed/size – but that is not specified by per the C spec. It must be 16 or more bits. int_fast16_t is most efficient type in speed with at least the range of a 16 bit int. Example: A given platform may have decided that int should be 32-bit … Read more
If you spend a little time in the library, you don’t have to speculate. Here are some statements taken from Dennis Ritchie’s paper on the evolution of C. The context is that Dennis is building on Ken Thompson’s language B, which was implemented on the very tiny PDP-7, a word-addressed machine. Because of growing interest, … Read more
In the very beginning of C the available memory and CPU resources were really scarce. So it had to compile really fast with minimal memory requirements. Therefore the C language has been designed to require only a very simple compiler which compiles fast. This in turn lead to “single-pass compiler” concept: The compiler reads the … Read more
There may be some confusion here about what “K&R C” is. The term refers to the language as documented in the first edition of “The C Programming Language.” Roughly speaking: the input language of the Bell Labs C compiler circa 1978. Kernighan and Ritchie were involved in the ANSI standardization process. The “ANSI C” dialect … Read more
There is in C99, but not in previous standards AFAIK. In C99, you’ll have NAN and INFINITY macros. From “Mathematics <math.h>“ (§7.12) section The macro INFINITY expands to a constant expression of type float representing positive or unsigned infinity, if available; … If you’re stuck with ANSI C89, you’re out of luck. See C-FAQ 14.9.