minus number from cell and result in specific cell and specific column

[voltaire101]

What is the formulas for these two questions

First question

What I want is like this

I have number in cell (A1) = 100
when I enter number in any cell of column(B) for example (B1)=10
then in cell (C1) the result of (A1) - (B1) = (90)

and if I add in cell (B2)=10
then in cell (C1) the result of (A1) - (B1+B2) = 80 .accumulatively in cell (C1)

and any number in column (B), the result will be (A1) minus any number in column(B) accumulated in (C1)

<<<<<<<<<<<<<<<<<<<

second question

As above, but some thing is different which is

I have number in cell (A1) = 100
when I enter number at cell (B1) = 10
then the result would be in the adjacent cell (C1) = (A1) - ( B1) = 90
and If I enter a new number in cell (B2) = 10
then the result would be in the adjacent cell (C2) = (A1) - (B1+B2) = 80
and If I enter a new number in cell (B3) = 10
then the result would be in the adjacent cell (C3) = (A1) - (B1+B2+B3) = 70
and so on ..

I want the result to be add automatically to adjacent cell in column (C)