diff options
| -rw-r--r-- | c.html.markdown | 48 |
1 files changed, 31 insertions, 17 deletions
diff --git a/c.html.markdown b/c.html.markdown index a57be1dc..ff396d21 100644 --- a/c.html.markdown +++ b/c.html.markdown @@ -224,10 +224,18 @@ int main (int argc, char** argv) (float)i1 / i2; // => 0.5f i1 / (double)i2; // => 0.5 // Same with double f1 / f2; // => 0.5, plus or minus epsilon + // Floating-point numbers and calculations are not exact + // for instance it is not giving mathematically correct results + (0.1 + 0.1 + 0.1) != 0.3; // => 1 (true) + // and it is NOT associative + 1 + (1e123 - 1e123) != (1 + 1e123) - 1e123; // => 1 (true) + // this notation is scientific notations for numbers: 1e123 = 1*10^123 - // Modulo is there as well - 11 % 3; // => 2 + // Modulo is there as well, but be careful if arguments are negative + 11 % 3; // => 2 as 11 = 2 + 3*x (x=3) + (-11) % 3; // => -2, as one would expect + 11 % (-3); // => 2 and not -2, and it's quite counter intuitive // Comparison operators are probably familiar, but // there is no Boolean type in C. We use ints instead. @@ -236,12 +244,12 @@ int main (int argc, char** argv) // operators always yield 0 or 1.) 3 == 2; // => 0 (false) 3 != 2; // => 1 (true) - 3 > 2; // => 1 - 3 < 2; // => 0 + 3 > 2; // => 1 + 3 < 2; // => 0 2 <= 2; // => 1 2 >= 2; // => 1 - // C is not Python - comparisons don't chain. + // C is not Python - comparisons do NOT chain. // Warning: The line below will compile, but it means `(0 < a) < 2`. // This expression is always true, because (0 < a) could be either 1 or 0. // In this case it's 1, because (0 < 1). @@ -349,25 +357,30 @@ int main (int argc, char** argv) break; } /* - using "goto" in C + Using "goto" in C */ typedef enum { false, true } bool; // for C don't have bool as data type before C99 :( bool disaster = false; int i, j; - for(i=0;i<100;++i) - for(j=0;j<100;++j) + for(i=0; i<100; ++i) + for(j=0; j<100; ++j) { if((i + j) >= 150) disaster = true; if(disaster) - goto error; + goto error; // exit both for loops } - error : + error: // this is a label that you can "jump" to with "goto error;" printf("Error occurred at i = %d & j = %d.\n", i, j); /* - https://ideone.com/GuPhd6 - this will print out "Error occurred at i = 51 & j = 99." + https://ideone.com/GuPhd6 + this will print out "Error occurred at i = 51 & j = 99." + */ + /* + it is generally considered bad practice to do so, except if + you really know what you are doing. See + https://en.wikipedia.org/wiki/Spaghetti_code#Meaning */ /////////////////////////////////////// @@ -741,11 +754,12 @@ typedef void (*my_fnp_type)(char *); // Order of Evaluation /////////////////////////////////////// +// From top to bottom, top has higher precedence //---------------------------------------------------// // Operators | Associativity // //---------------------------------------------------// // () [] -> . | left to right // -// ! ~ ++ -- + = *(type)sizeof | right to left // +// ! ~ ++ -- + = *(type) sizeof | right to left // // * / % | left to right // // + - | left to right // // << >> | left to right // @@ -783,8 +797,8 @@ as the C file. /* included into files that include this header. */ #include <string.h> -/* Like c source files macros can be defined in headers and used in files */ -/* that include this header file. */ +/* Like for c source files, macros can be defined in headers */ +/* and used in files that include this header file. */ #define EXAMPLE_NAME "Dennis Ritchie" /* Function macros can also be defined. */ @@ -823,7 +837,7 @@ Best to find yourself a copy of [K&R, aka "The C Programming Language"](https:// It is *the* book about C, written by Dennis Ritchie, the creator of C, and Brian Kernighan. Be careful, though - it's ancient and it contains some inaccuracies (well, ideas that are not considered good anymore) or now-changed practices. -Another good resource is [Learn C The Hard Way](http://learncodethehardway.org/c/). +Another good resource is [Learn C The Hard Way](http://learncodethehardway.org/c/) (not free). If you have a question, read the [compl.lang.c Frequently Asked Questions](http://c-faq.com). @@ -833,4 +847,4 @@ Readable code is better than clever code and fast code. For a good, sane coding Other than that, Google is your friend. -[1] [Why isn't sizeof for a struct equal to the sum of sizeof of each member?](http://stackoverflow.com/questions/119123/why-isnt-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member) +[1] [Why isn't sizeof for a struct equal to the sum of sizeof of each member?](https://stackoverflow.com/questions/119123/why-isnt-sizeof-for-a-struct-equal-to-the-sum-of-sizeof-of-each-member) |