It is possible to initialize an array during declaration. For example,
int mark[5] = {19, 10, 8, 17, 9};
You can also initialize an array like this.
int mark[] = {19, 10, 8, 17, 9};
Here, we haven’t specified the size. However, the compiler knows its size is 5 as we are initializing it with 5 elements.

Here,
mark[0] is equal to 19 mark[1] is equal to 10 mark[2] is equal to 8 mark[3] is equal to 17 mark[4] is equal to 9