How to Find the Size of an Array in C?

The size of an array is generally considered to be the number of elements in the array (not the size of memory occupied in bytes). In this article, we will learn how to find the size of an array in C.

The simplest method to find the size of an array in C is by using sizeof operator. First determine the total size of the array in bytes and divide it by the size of one element to get the number of elements.

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40, 50};

    // Total size divided by size of one element
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("%d\n", n);
    return 0;
}

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There is also one more method is C that can be used to find the size of an array in C.

Using Pointer Arithmetic

The idea is to use pointer arithmetic to find the difference between the memory addresses of the first element of the array and the beyond the last which will be then automatically scaled by the compiler according to the type of array.

#include <stdio.h>

int main() {
    int arr[] = {10, 20, 30, 40, 50};

    // Calculate the size
    int n = *(&arr + 1) - arr;

    printf("%d\n", n);
    return 0;
}

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Note: All these methods only work as long as the array has not decayed into a pointer. Once it decays, it is treated as a pointer, and the size of the array can no longer be determined.