How to make the value of one Cell as a position of another Cell in Excel

Question

In Excel, lets say,

    A    B
1   10   4
2   20   1
3   30   2
4   40   3

Here values in COL B is changing every time interval so in this instance:
B1 = 4, so in Cell C1, I want to use B1's value as pointer to COL A's position
i.e I want value of A4 in C1 i.e C1 should display 40.
Similarly, C2 will carry A1 value, i.e. C2 should display 10
Similarly, C4 will carry A3 value, i.e. C4 should display 30

I do not want to use vb scripts. Thank you in advance.

Answer 1

Use the INDEX() Function:

=INDEX(A:A,B1)