C Arrays
Arrays
Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.
To create an array, define the data type (like int) and specify the name
of the array followed by square brackets [].
To insert values to it, use a comma-separated list inside curly braces, and make sure all values are of the same data type:
int myNumbers[] = {25,
50, 75, 100};
We have now created a variable that holds an array of four integers.
Access the Elements of an Array
To access an array element, refer to its index number.
Array indexes start with 0: [0] is the first element. [1] is the second element, etc.
This statement accesses the value of the first element [0] in
myNumbers:
Example
int myNumbers[] = {25, 50, 75, 100};
printf("%d", myNumbers[0]);
// Outputs 25
Try it Yourself »
Change an Array Element
To change the value of a specific element, refer to the index number:
Example
myNumbers[0] = 33;
Example
int myNumbers[] = {25, 50, 75, 100};
myNumbers[0] = 33;
printf("%d", myNumbers[0]);
// Now outputs 33 instead of 25
Try it Yourself »
Loop Through an Array
You can loop through the array elements with the for
loop.
The following example outputs all elements in the myNumbers
array:
Example
int myNumbers[] = {25, 50, 75, 100};
int i;
for (i = 0; i < 4; i++)
{
printf("%d\n", myNumbers[i]);
}
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Set Array Size
Another common way to create arrays, is to specify the size of the array, and add elements later:
Example
// Declare an array of four integers:
int myNumbers[4];
// Add
elements
myNumbers[0] = 25;
myNumbers[1] = 50;
myNumbers[2] = 75;
myNumbers[3] = 100;
Try it Yourself »
Using this method, you should know the number of array elements in advance, in order for the program to store enough memory.
You are not able to change the size of the array after creation.
Avoid Mixing Data Types
It is important to note that all elements in an array must be of the same data type.
This means you cannot mix different types of values, like integers and floating point numbers, in the same array:
In the example above, the values 3.15 and 5.99 will be truncated to 3 and 5. In some cases it might also result in an error, so it is important to always make sure that the elements in the array are of the same type.
