Finding the Array Size

Finding the Array Size

You don't need to count elements by hand: sizeof can tell you the array length.

The trick

Divide the total bytes by the bytes of one element:

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

printf("%d", length);   // 5

• sizeof(myNumbers) = bytes of the whole array.
• sizeof(myNumbers[0]) = bytes of one int.
• Divide them to get the element count.

Loop with the computed size

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

No hard-coded counting, easy to change the array.

When it doesn't work

The trick works only on the array itself inside its own scope. Passed to a function as a parameter, the array "decays" to a pointer, so sizeof no longer gives the full size.

TL;DR

• size = sizeof(arr) / sizeof(arr[0]).
• Loop with the computed length instead of hard-coding.
• Update the array and the loop adapts.
• Lost size is a pointer thing - more on functions later.