C Array Size

Get Array Size or Length

To get the size of an array, you can use the sizeof operator:

– It is because the sizeof operator returns the size of a type in bytes.

You learned from the Data Types article that an int type is usually 4 bytes, so from the example above, 4 x 5 (4 bytes x 5 elements) = 20 bytes.

Knowing the memory size of an array is great when you are working with larger programs that require good memory management.

But when you just want to find out how many elements an array has, you can use the following formula (which divides the size of the array by the size of the first element in the array):

int myNumbers[] = {10, 25, 50, 75, 100};
int length = sizeof(myNumbers) / sizeof(myNumbers[0]);

printf("%d", length);  // Prints 5

Making Better Loops

In the array loops section in the previous article, we wrote the size of the array in the loop condition (i
< 4). This is not ideal, since it will only work for arrays of a specified size.

However, by using the sizeof formula from the example above, we can now make loops that work for arrays of any size, which is more sustainable.

Instead of writing:

int myNumbers[] = {25, 50, 75, 100};
int i;

for (i = 0; i < 4; i++) {
  printf("%d\n", myNumbers[i]);
}

It is better to write:

int myNumbers[] = {25, 50, 75, 100};
int length = sizeof(myNumbers) / sizeof(myNumbers[0]);
int i;

for (i = 0; i < length; i++) {
  printf("%d\n", myNumbers[i]);
}