C variables

Main Types

numbers

// numbers
int    num = 3;
float  num = 3.045f;			// f is optional, but ensures the value is a float vs double
double num = 2.4056;
long   num = 2.0000;			// bigger than double

strings

// strings
char   letter = 'A';					// chars use single-quotes
char  *name   = "will";				// Another way to create a string
char   name[] = "will";				// C does not have the concept of strings, it uses arrays of chars
											// ending in '\0'

char *names[] = {"abc","def"};	// arrays of cstrings require a *

arrays

// arrays
int    num[] = { 1, 2, 3, 4 };	//array

pointers

// pointers
void run_function( struct MyStruct mystruct ){
	printf("test");
}

int *ptr = malloc( sizeof(struct MyStruct) );	// get pointer to struct of type 'MyStruct'
run_function( &my_struct );

structs

Simple usage of a struct:

struct MyStruct {
	int a;
	int b;
};

struct MyStruct var;
var.a = 5;
var.b = 10;

print( var.a );

Structs do not let you assign variables where they are being defined. The following example provides a workaround, effectively creating a constructor for the struct.

// struct
/*
 * Structs get a little more complicated, because you manually need to
 * allocate memory, and create your own constructor.
 *
 */

struct Person {
	char *name;
	int  age;
	int  height;
	int  weight;
};


struct Person *Person_create( char *name, int age, int height, int weight ){
	/*
	 * Creates new struct, and initializes it's attrs.
	 * (basically, this is a constructor for 'Person')
	 */
	struct Person *who = malloc( sizeof(struct Person ) );
	assert(who != NULL);

	who->name   = strdup(name);	// create new copy in memory
	who->age    = age;
	who->height = height;
	who->weight = weight;

	return who;
}

void Person_destroy(struct Person *who){
	/*
	 * Pass ptr 'who' to this function, and 
	 * the object will be deleted in memory
	 *
	 */

	 assert(who != NULL);
	 free(who->name);	// delete string separately, it has it's own independent location.

}


struct Person {
	char *name;
	int   age;
	int   height;
	int   weight;
};

struct Person *will = Person_create( "will" );	// your constructor returns a pointer. Create a pointer to
																// the variable with the type 'Person'

Format Strings

printf("string: %s", str );						//string
printf("char:   %c", chr );						//char
printf("int:    %d", num );						//int
printf("ptr:    %p", ptr );						//pointer
printf("sizeof: %lu", sizeof(my_string) );	//unsigned-long