diff options
Diffstat (limited to 'c.html.markdown')
| -rw-r--r-- | c.html.markdown | 47 |
1 files changed, 30 insertions, 17 deletions
diff --git a/c.html.markdown b/c.html.markdown index 8e170300..d3f20eda 100644 --- a/c.html.markdown +++ b/c.html.markdown @@ -4,6 +4,8 @@ filename: learnc.c contributors: - ["Adam Bard", "http://adambard.com/"] - ["Árpád Goretity", "http://twitter.com/H2CO3_iOS"] + - ["Jakub Trzebiatowski", "http://cbs.stgn.pl"] + - ["Marco Scannadinari", "https://marcoms.github.io"] --- @@ -20,13 +22,19 @@ memory management and C will take you as far as you need to go. Multi-line comments look like this. They work in C89 as well. */ - // Constants: #define <keyword> +/* +Multi-line comments don't nest /* Be careful */ // comment ends on this line... +*/ // ...not this one! + +// Constants: #define <keyword> #define DAYS_IN_YEAR 365 - // Enumeration constants are also ways to declare constants. - enum days {SUN = 1, MON, TUE, WED, THU, FRI, SAT}; +// Enumeration constants are also ways to declare constants. +// All statements must end with a semicolon +enum days {SUN = 1, MON, TUE, WED, THU, FRI, SAT}; // MON gets 2 automatically, TUE gets 3, etc. + // Import headers with #include #include <stdlib.h> #include <stdio.h> @@ -51,7 +59,6 @@ int main() { // print output using printf, for "print formatted" // %d is an integer, \n is a newline printf("%d\n", 0); // => Prints 0 - // All statements must end with a semicolon /////////////////////////////////////// // Types @@ -73,12 +80,12 @@ int main() { long long x_long_long = 0; // floats are usually 32-bit floating point numbers - float x_float = 0.0; + float x_float = 0.0f; // 'f' suffix here denotes floating point literal // doubles are usually 64-bit floating-point numbers - double x_double = 0.0; + double x_double = 0.0; // real numbers without any suffix are doubles - // Integral types may be unsigned. + // integer types may be unsigned (greater than or equal to zero) unsigned short ux_short; unsigned int ux_int; unsigned long long ux_long_long; @@ -175,6 +182,9 @@ int main() { i2 * i1; // => 2 i1 / i2; // => 0 (0.5, but truncated towards 0) + // You need to cast at least one integer to float to get a floating-point result + (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 @@ -194,9 +204,11 @@ int main() { 2 >= 2; // => 1 // C is not Python - comparisons don't chain. - // WRONG: - //int between_0_and_2 = 0 < a < 2; - // Correct: + // 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). + int between_0_and_2 = 0 < a < 2; + // Instead use: int between_0_and_2 = 0 < a && a < 2; // Logic works on ints @@ -211,7 +223,7 @@ int main() { int e = 5; int f = 10; int z; - z = (a > b) ? a : b; // => 10 "if a > b return a, else return b." + z = (e > f) ? e : f; // => 10 "if e > f return e, else return f." //Increment and decrement operators: char *s = "iLoveC"; @@ -222,7 +234,7 @@ int main() { // same with j-- and --j // Bitwise operators! - ~0x0F; // => 0xF0 (bitwise negation, "1's complement") + ~0x0F; // => 0xFFFFFFF0 (bitwise negation, "1's complement", example result for 32-bit int) 0x0F & 0xF0; // => 0x00 (bitwise AND) 0x0F | 0xF0; // => 0xFF (bitwise OR) 0x04 ^ 0x0F; // => 0x0B (bitwise XOR) @@ -230,7 +242,7 @@ int main() { 0x02 >> 1; // => 0x01 (bitwise right shift (by 1)) // Be careful when shifting signed integers - the following are undefined: - // - shifting into the sign bit of a signed integer (int a = 1 << 32) + // - shifting into the sign bit of a signed integer (int a = 1 << 31) // - left-shifting a negative number (int a = -1 << 2) // - shifting by an offset which is >= the width of the type of the LHS: // int a = 1 << 32; // UB if int is 32 bits wide @@ -374,7 +386,8 @@ int main() { // or when it's the argument of the `sizeof` or `alignof` operator: int arraythethird[10]; int *ptr = arraythethird; // equivalent with int *ptr = &arr[0]; - printf("%zu, %zu\n", sizeof arraythethird, sizeof ptr); // probably prints "40, 4" or "40, 8" + printf("%zu, %zu\n", sizeof arraythethird, sizeof ptr); + // probably prints "40, 4" or "40, 8" // Pointers are incremented and decremented based on their type @@ -465,7 +478,7 @@ void testFunc() { } //make external variables private to source file with static: -static int j = 0; //other files using testFunc() cannot access variable i +static int j = 0; //other files using testFunc2() cannot access variable j void testFunc2() { extern int j; } @@ -573,7 +586,7 @@ typedef void (*my_fnp_type)(char *); '\''; // single quote '\"'; // double quote '\xhh'; // hexadecimal number. Example: '\xb' = vertical tab character -'\ooo'; // octal number. Example: '\013' = vertical tab character +'\0oo'; // octal number. Example: '\013' = vertical tab character //print formatting: "%d"; // integer @@ -618,7 +631,7 @@ typedef void (*my_fnp_type)(char *); ## Further Reading Best to find yourself a copy of [K&R, aka "The C Programming Language"](https://en.wikipedia.org/wiki/The_C_Programming_Language) -It is *the* book about C, written by the creators of C. Be careful, though - it's ancient and it contains some +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://c.learncodethehardway.org/book/). |