In C, are arrays pointers or used as pointers?

Question

My understanding was that arrays were simply constant pointers to a sequence of values, and when you declared an array in C, you were declaring a pointer and allocating spac

Answer 1

sizeof is evaluated at compile-time, and the compiler knows whether the operand is an array or a pointer. For arrays it gives the number of bytes occupied by the array. Your array is a char[] (and sizeof(char) is 1), thus sizeof happens to give you the number of elements. To get the number of elements in the general case, a common idiom is (here for int):

int y[20];
printf("number of elements in y is %lu\n", sizeof(y) / sizeof(int));

For pointers sizeof gives the number of bytes occupied by the raw pointer type.