An vector of   int named  a that contains exactly five elements has already been declared and initialized. in addition, an   int variable   j has also been declared and initialized to a value somewhere between 0 and 3. 
write a single statement that assigns a new value to the element of the vector indexed by   j . this new value should be equal to twice the value stored in the next element of the vector (i. e. the element after the element indexed by   j ).  do not modify any other elements of the vector!