find length of array in c

1int a[20];
2int length;
3length = sizeof(a) / sizeof(int);
4

1int prices[5] = { 1, 2, 3, 4, 5 };
2
3int size = sizeof prices / sizeof prices[0];
4
5printf("%u", size); /* 5 */

1int a[17];
2size_t n = sizeof(a)/sizeof(a[0]);
3

1int a[17];
2size_t n = sizeof(a)/sizeof(a[0]);

1int a[]= { 1, 2, 3, 4, 5, 6, 7 };
2int length = sizeof(a) / sizeof(a[0]); //return 7

1int a[17]; // initializing an array
2int length = sizeof(a)/sizeof(a[0]); // divide array size(in byte)/ size of the first element of the array of the same type, here int(integer size is 4byte)