Doubt regarding declaration of array

#1

hey!
the constraint given for N in the question is==> " 1 <= N <= 100000 ".
Q1) how should i declare my array in the main function??
Q2) is it right to declare the array as int arr[100000] in the main function ?
Q 3) can we declare as int arr[100] ? if no,why not ?

#2

you have to declare in this fashion
int arr[100000];
because no of elements are upto this value
if you declare arr[100] then you can store only 100 element