why does EIP register updates it value after executing each instruction? write the steps of executing for the following instruction: ADD eax, var2

following code contains:

var1 DWORD 10h

var2 DWORD 20h

var3 DWORD 30h

var4 DWORD 40h

write code to exchange the values among variable only use one temporary storage: variable or register can only use MOV or XCHG after executon var1 = 20h, var2=40h, var3=10h and var4=30h