C

Hello World

#include <stdio.h>

int main()
{
  printf(“Hello, world!”);
  return 0;
}

Variable Declaration

Note that C is statically typed.

int days_in_week = 7;
float cm_to_in = 2.54;
char the_w = 'W';

printf("%d days in a week.\n", days_in_week);
printf("%f cm per in.\n", cm_to_in);
printf("The %c is a cool hotel.\n", the_w);

Arrays

Note that the size of the array is declared at initialization.

float numbers[3];
numbers[0] = 3.1415;
numbers[1] = 1.618;
numbers[2] = 1.4142;

Leave the size blank for unlimited size

int lots_of_nums[];

Note that when initialized curly brackets are used, not square brackets!!

int fibs[] = {1, 1, 2, 3, 5};

Strings are represented as an array of chars

char word[] = “applesauce”;

Operators & Expressions

%        modulo

+=        assignment operators
-=
*=
/=

n++;        auto increment (if assigned, performed after assignment)
n—-;        auto decrement (if assigned, performed after assignment)
++n;        auto increment (if assigned, performed before assignment)
—n;         auto decrement (if assigned, performed before assignment)

e.g.

int a = 3;
int b = a++; // n == 3, a == 4
int c = —-a; // c == 3, a == 3

Loops

for (int i = 0; i < 10; i++) {
  printf(“%d”, i);
}

while (done == false) {
  // do something
}

do {
  // do-while, a reverse while.
  // useful if we want to evaluate the block before checking the conditional.
} while (done == false);

Conditionals & Switch Statements

if (conditional) {

} else if (another) {

} else {

}

One line conditional. Note that you can add else-ifs as well, unlike in Ruby:

if (1 == 1) printf(“1 is equal to 1”);
else if (1 > 1) printf(“Boy is this strange”);

Switch statement:

switch (value) {
  case ‘a’:
    printf(“It’s ‘a’”);
    break;

  case ‘b’:
    printf(“It’s ‘b’”);
    break;

  default:
    printf(“It’s neither ‘a’ nor ‘b’”);
    break;
}

Functions

Note that the return type is statically declared (here it is ‘int’).

int doubler(int n) {
  return n*2;
}

If a function has no return type, use ‘void’

void hello() {
  printf(“Hello, I am a computer”);
}

Scope

Scope in C is lexical; that is, scope is defined by what is between a set of brackets {}. Similar in practice to Ruby’s block-level scope. Contrast this with Javascript, which has functional scope.

Pointers & Memory

Pointers point to the memory address of a variable.

char *letter;  // * indicates that this is a pointer type
char k = ‘k’;
letter = &k;  // this points to the memory address of k, not the value of k.
printf(“%c”, *letter);  => k
k = ‘x’;
printf(“%c”, *letter);  => x // the address is the same, but the value has changed.

Using pointers to traverse arrays

int nums[3] = {3, 5, 7};
num = &nums[0];
printf(“%d”, *num)  => 3
++num; // increment the pointer to the next address in memory!
printf(“%d”, *num)  => 5

Calculating the length of an array using sizeof():

printf(“float size: %ld bytes\n”, sizeof(1.5));  =>  float size: 4 bytes

long floatArrayLength(float array) {
 long element_size = sizeof(array[0]);
 return sizeof(array) / element_size;
}

C

C