Arrays

An array variable is a collection of elements laid out consecutively in memory. All elements have the same declared type. Individual elements are accessed with the [] notation must come after the variable name. The actual value of an array variable is a memory address in C.

This is the declaration of an array that can hold 12 integer values:

int c[12]

The first element can be accessed with c[0] and the last element is always one less than the size of the array (i.e., c[11]). Assign a value to an element with c[0]=7.

If you try to access your array before initializing, then do not know what value the elements will have and you will get warnings.

Initializing Arrays

With a for loop:

int c[12]; // elements undefined
for (int i = 0; i < 12; i++) {
	c[i] = i; // initialize with value matching index number
}

With literal values by using values separated by commas within { ... }. Array size can be omitted when initializing with { ... }.

int c[5] = {2, 4, 6, 8, 10};

c[ ] = {2, 4, 6, 8} // no size

Whole Array Operations (NOT)

• There is no "slicing" in C. (E.g., can't access several elements using c[1:4]).
• Cannot print (printf("%a", c)) or read (scanf("%a", c)) a entire entire array (except for char arrays).

Strings

Strings are a sequence of characters handled as a unit; not a separate type. It is an array of characters with the final character equal to the "null character", \0, also called the "null terminator," and has the first character on the ASCII table with a value of 0.

Two declarations of string. The first declaration shows a string is like an array. The second uses an array with the final character equal to the "null character” and both first and second strings are null-terminated and are arrays of size 7. The third declaration shows a string is like a pointer.

char day[] = "monday";

// same as
char day[] = {'m', 'o', 'n', 'd', 'a', 'y', '\0'}

//alteratively
const char *day_ptr "monday";

String Character Access

Indexing, or accessing elements of the string utilizes square bracket notation.

cnst char str[] = "hello";
print("%c %c \n", str[1], str[2]) // prints "e l"

Printing Strings

Strings are an array of null-terminated (\n) characters. Null termination is used to indicate where the string ends, so it will only print chars up to the (first) \n.

printf("%s", s);

String Functions

Size-related functions that return an unsigned long (%lu format string).

• strlen function returns number of chars before \n. (best way to find length of a given variable). From the #inlude <string.h> library.
• sizeof function returns amount of space occupied by a variable; the total # of bytes.
  • sizeof(type_name) like int it tells you how many bytes an integer type is. sizeof(array_var) also tells you is declared size.
  • If you had an array named ra of 5 integers, sizeof(ra) / sizeof(int) would tell you the size of the given array. Works with any type.

#include<string.h> includes helpful string functions:

• strcmp(s1, s2) compares two strings according to character ASCII values.
  • Negative value: s1 before s2, Zero: s1 and s2 are equal. Positive: s1 after s2.
• strcpy(s1, s2) copy effect is like s1 = s2 as long as s1 is declared with a sufficient size to fit s2.
• strcat(s1, s2) concatenate effect is like s1 = s1 + s2 as long as s1 is declared with a sufficient size.
• See more: strncpy, strncat, strtok, and others.

String Operations (NOT)

• There is no concatenation operator +.
• No assignment = between strings declared as arrays. You cannot do a whole assignment into an array because it is a fixed memory address.
• Assignment is allowed between strings declared as pointers.