Static variable in solidity?

Question

I define a balance as follows :

mapping (address => uint[]) Energy_Balance

to keep the history of each transaction. I set its new value as follows :

First Transaction: balances[owner][0] = balances[owner][0] + value; 
Second Transaction: balances[owner][1] = balances[owner][1] + value;

Now, I want to define a uint counter such that it can keep its last value every time it is increased one unit as follows :

balances[owner][counter] = balances[owner][counter] + value

If I define counter as follows, is it correct in solidity and it can keep its last value ?

static uint counter = 0;
function myFunction(uint value) {
    balances[owner][counter] = balances[owner][counter] + value;
    counter = counter +1;
}

Answer 1

You can simplify.

function myFunction(uint value) {
  balances[owner].push(value);
}

Also, some useful getters:

function getOwnerValueCount(address owner) returns(uint count) {
  return balances[owner].length;
}

Add public to your mapping for Energy_Balances and you will get a "free" getter approximately:

function Energy_Balances(address owner, uint row) public view returns(uint) {
  return Energy_Balances[owner][row];
}

Aside: It would be more conventional to camelCase energyBalances.

Hope it helps.