int arr$[10]=\{100,90,80,70,60,50,40,30,20,10\}$;

For the above declared integer array of size $10($that is$,$ the array holds $10$ integer elements$),$ the last element in the array has an index of $10.$ That is$,$ we could access its value $($which coincidentally is also $10)$ and display it to the console as follows:

cout $<<$ arr$[10]$;