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Arrays and strings - C

3 min read

Arrays

A sequence of values back to back (contiguous) in memory all of which is the same data type

Declaration

  • type name[size];
    • Telling the compiler that this is an array of integers of size size
    • The elements in the array are all contiguous in memory
# individual element syntax
int scores[3];
scores[0] = 72;
scores[1] = 73;
scores[2] = 33;
 
# instantiatino syntax
bool truthtable[3] = {false, true, true}
bool truthtable[] = {false, true, true} 
// size is optional in instantiatino syntax
  • In C, if you pass an array as input to a function, you don’t have to know in advance what the size is
  • BUT so actually u need to pass in how big it is in the function too (int length in this example)
const int length = 5;
int scores[3] = {1,2,3};
average(length, scores);
 
float average(int length, int array[]) { // pass in length as well
	int sum = 0;
	for (int i = 0; i < length; i++) {
		sum += array[i];
;	}
return sum / (float) length;
}

String

#include <stdio.h>
 
int main(void)
{
    char c1 = 'H';
    char c2 = 'I';
    char c3 = '!';
 
    printf("%i %i %i\n", c1, c2, c3);
}

  • If you do this, then ASCII codes are being printed

  • String is actually an array of chars

string s = "HI!";
printf("%c %c %c", s[0], s[1], s[2]);
  • use string.h

Other examples

int main(void)
{
    string words[2];
 
    words[0] = "HI!";
    words[1] = "BYE!";
 
    printf("%s\n", words[0]);
    printf("%s\n", words[1]);
    // same with
	printf("%c%c%c\n", words[0][0], words[0][1], words[0][2]);
    printf("%c%c%c%c\n", words[1][0], words[1][1], words[1][2], words[1][3]);
 
}

NUL

  • the last byte of a string will always be 0, a special delimiting character NUL
string s = "HI!";
printf("%i %i %i %i\n", s[0], s[1], s[2], s[3]); // 72 73 33 \0
  • the variable indicate where the string begins, the\0 indicate where the string ends
    • Every string’s actual length is length + 1
  • The double quotes imply that it’s a string & it needs to be terminated with backslash 0
int main(void)
{
	string s = get_string("Input: ");
	printf("Output: ");
	// inititalize strlen here too!!
	for (int i = 0, n = strlen(s); i < n; i++)
	{
		printf("%c", s[i]);
	}
	print("\n");
}

📌Determining the NUL terminator

  • As a String: Functions like printf("%s") or strlen() are specifically built to stop the moment they see the first \0. To them, this 0 means “end of string”.
  • As an Array: When you use a for loop (e.g., for (int i = 0; i < 10; i++)), you are in charge. You tell it the exact length, so it treats the 0 just like any other number and keeps going.

Multi-dimension

  • Arrays can consist of more than a single dimension
    • You can have as many size specifiers as you wish
  • bool battleship[10][10]
    • 10 x 10 grid of cells
    • In memory though, it’s just a 100-element 1D array
  • Multi-dimensional arrays are great abstractions to help visualize gameboards or other complex representations
  • We can’t treat entire arrays themselves as variables
    • we CANNOT assign one array to another using the assignment operator (not legal C)
    • we must use a loop to copy over the elements one at a time

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