[Cpp-Programming] To find out process size

How to find out size of the specific process........ yeah, from the
task manager we can get it but not that one what i want.......

I want why any process takes that much amount of memory..... with a
real time example.........

for eg svchost.exe normally takes approx. 30Mb of main memory
amount....... why it takes 30Mb and what is the process, an elaborate
explanation i want.........