Final answer:
The line "*(myarray + 1) = 100;" is a legal operation in C/C++ that assigns the value 100 to the second element of the array named myarray.
Step-by-step explanation:
The expression "*(myarray + 1) = 100;" is indeed legal in the context of C or C++ programming. What this line of code does is it accesses the second element of the array myarray by using pointer arithmetic and assigns it the value of 100. In C and C++, the name of the array can be used as a pointer to the first element of the array. Therefore, when you add 1 to myarray, you are moving to the next element in the array. Dereferencing this pointer with an asterisk * allows you to modify the value at that memory address.