int arr1[] = {1,2,3,4,5}; char arr2[] = "hello"; int arr3[5] = {1,2}; int arr4[] = {};
arr1的长度为5，arr2的长度为5
arr3的长度为2，arr4的长度为0
arr2的长度为6，arr4的长度可被自动推导为0
arr1的长度为5，arr3的长度为5