Arrays

In the C language, an array is a list of values, with a fixed length.

Being able to store multiple pieces of related information in the same structure is very useful when writing C programs.

Declaring an Array

The syntax for declaring an array is first specify the data type, then a descriptive array name, followed by square brackets surrounding the array’s length (number of items):

type name[length];

To declare an int array named grades with a length of 6:

int grades[6]; // An array to hold six integers

Alternatively, the length can be omitted and the array’s initial values can be assigned to it instead. Values are assigned inside of the curly brackets and separated by commas.

int grades[] = {96, 90, 78, 84, 88, 92};

Accessing Values with Indexes

The values in arrays are accessed using their index, or their position in the array. They can either be assigned or used this way.

char vowels[] = {'a', 'e', 'i', 'o', 'u'};

Note that in C, an array’s indexes start at 0 instead of 1:

      +-------------------------+
Value | 'a'  'e'  'i'  'o'  'u' |
      +-------------------------+
Index |  0    1    2    3    4  |
      +-------------------------+

An element can be accessed by referring to the array name and the element’s index number:

• vowels[0] will give the value 'a'
• vowels[1] will give the value 'e'
• vowels[2] will give the value 'i'
• vowels[3] will give the value 'o'
• vowels[4] will give the value 'u'

char vowels[] = {'a', 'e', 'i', 'o', 'u'};

putchar(vowels[3]);
// Output: o

Example

Creating an array that holds the snowfall measurements (in the nearest inch) from the past 7 days:

#include <stdio.h>

int main() {
  int snowfall[] = {10, 13, 14, 11, 9, 8, 6};
  printf("%d\n", snowfall[0]);

  snowfall[2] = 16; // Update an element
  printf("%d\n", snowfall[2]);

  return 0;
}

The output would be:

10
16