I am learning c. I have the following code:

char s1[] = {'h', 'e', 'l', 'l', 'o'};
char s2[] = {'w', 'o', 'r', 'l', 'd'};

printf("Original strings:nt%snt%sn", s1, s2);

I expect the output to be

Original strings:
    hello
    world

The output is actually

Original strings:
    helloworld
    world

It appears that the first array is initialized without a null character '' at the end, while the second is initialized with a null character. The arrays are also put right next to each other in memory (I print the address, &s1[i], along with the value stored there, s1[i]):

0x7fffe344a98e  104     'h'
0x7fffe344a98f  101     'e'
0x7fffe344a990  108     'l'
0x7fffe344a991  108     'l'
0x7fffe344a992  111     'o'
0x7fffe344a993  119     'w' - not '' ?
0x7fffe344a994  111     'o'
0x7fffe344a995  114     'r'
0x7fffe344a996  108     'l'
0x7fffe344a997  100     'd'
0x7fffe344a998  0       ''

These conditions cause that the printf function prints helloworld instead of just hello for s1 because there is no null character until after ‘d’. If I delete s2, then s1 does initialize with a null character at the end and prints normally (using %s). I want to understand why c is deleting the null character after 'o' in s1 when I declare a second char array immediately after.

I can specify the size of both arrays (for instance, s1[6] = {'h', ...}), and my issue is resolved. However, I don’t understand why c is deleting the null character in s1, or just never placing it in memory, when I create two char arrays sequentially. Thank you.