What is the output of: printf("%d\n", sizeof(array)); for int array[10];?

The expression sizeof(array) in the context of int array[10]; returns the total size in bytes of the entire array, not just the number of elements it contains.

In C, an int typically occupies 4 bytes on most platforms (though this can vary depending on the architecture). Since the declared array has 10 integers, the total size of the array is calculated as:

[ \text{Number of elements} \times \text{Size of each element} = 10 \times 4 \text{ bytes} = 40 \text{ bytes} ]

Therefore, the output of the printf statement will be 40, which is why this choice is the correct answer. The output does not depend on the content of the array; it solely depends on the data type and the number of elements defined in the array.