Suppose an instruction takes four cycles to execute in a nonpipelined cpu: one cycle to fetch the instruction, one cycle to decode the instruction, one cycle to perform the alu operation, and one cycle to store the result. in a cpu with a four-stage pipeline, that instruction still takes four cycles to execute, so how can we say the pipeline speeds up the execution of the program?

It speeds up the execution because the four-stage pipelined processor can execute the 4 phases simultaneously in different instructions.

Explanation:

Usually, programs have many instructions, and plenty of then do not rely on other operation's result to be executed. Therefore, the pipelined processor can be fetching, decoding, performing operations and storing other instructions that are not in the same dependency chain at the same time.  

a variable of array type holds a reference of object

array are commonly used in computer program to organize data so that a related set of values

array are using zero base indexing it start with 0.

all component of array have same type, two different types doesn't use in single array

if array are store 10 quantities its index value varies from 0 to 9.

it stores 1st quantity value in index value 0 and this process will same till index value 9.