diff options
| -rw-r--r-- | c.html.markdown | 46 |
1 files changed, 39 insertions, 7 deletions
diff --git a/c.html.markdown b/c.html.markdown index ec5c5e0d..8e16837c 100644 --- a/c.html.markdown +++ b/c.html.markdown @@ -1,10 +1,12 @@ --- -name: c -category: language -language: c -filename: learnc.c -contributors: - - ["Adam Bard", "http://adambard.com/"] +- name: c +- category: language +- language: c +- filename: learnc.c +- contributors: + - [Adam Bard](http://adambard.com/) + - [Árpád Goretity](http://twitter.com/H2CO3_iOS) + --- Ah, C. Still **the** language of modern high-performance computing. @@ -152,7 +154,7 @@ int main() { // So string literals are strings enclosed within double quotes, but if we have characters // between single quotes, that's a character literal. - // It's of type `int`, and *not* `char` (for hystorical reasons). + // It's of type `int`, and *not* `char` (for historical reasons). int cha = 'a'; // fine char chb = 'a'; // fine too (implicit conversion from int to char - truncation) @@ -176,6 +178,7 @@ int main() { // Comparison operators are probably familiar, but // there is no boolean type in c. We use ints instead. + // (Or _Bool or bool in C99.) // 0 is false, anything else is true. (The comparison // operators always yield 0 or 1.) 3 == 2; // => 0 (false) @@ -185,6 +188,13 @@ int main() { 2 <= 2; // => 1 2 >= 2; // => 1 + // C is not Python - comparisons don't chain. + int a = 1; + // WRONG: + int between_0_and_2 = 0 < a < 2; + // Correct: + int between_0_and_2 = 0 < a && a < 2; + // Logic works on ints !3; // => 0 (Logical not) !0; // => 1 @@ -201,6 +211,12 @@ int main() { 0x01 << 1; // => 0x02 (bitwise left shift (by 1)) 0x02 >> 1; // => 0x01 (bitwise right shift (by 1)) + // Be careful when shifting signed integers - the following are all undefined behavior: + // - shifting into the sign bit of a signed integer (int a = 1 << 32) + // - left-shifting a negative number (int a = -1 << 2) + // - shifting by an offset which is more than or equal to the width of the type of the LHS: + // int a = 1 << 32; // UB if int is 32 bits wide + /////////////////////////////////////// // Control Structures /////////////////////////////////////// @@ -237,6 +253,22 @@ int main() { printf("\n"); + // branching with multiple choices: switch() + switch (some_integral_expression) { + case 0: // labels need to be integral *constant* epxressions + do_stuff(); + break; // if you don't break, control flow falls over labels - you usually don't want that. + case 1: + do_something_else(); + break; + default: + // if `some_integral_expression` didn't match any of the labels + fputs("error!\n", stderr); + exit(-1); + break; + } + + /////////////////////////////////////// // Typecasting /////////////////////////////////////// |