Please make a Buy/sell script with lot size calculator

Looking for BUY/SELL script with lot size calculator.
Example:
BUY/SELL 2% based on previous candle's HIGH/LOW.
If HIGH/LOW is above 50 pips we devide by 2. So SL would be 25 pips. if hits our SL of 25 pips we lose 2%.

If HIGH/LOW is below 49 pips we stick with the 49 pips instead of deviding.

Attaching a screenshot...
Two red lines represents the openning a trade and SL.
69pips between the Openning trade and previous candle's High. It is above 50 pips so we devide by 2 which we will get around 34 pips of Stop Loss.
If our balance is 200$ then we risk 2% =4$ for 34 pips.
I hope I was clear

Dear Togu

Here's my lot sizing script. It is a lot more versatile than you really need for your requirement but it should be very easy to tweak if you want to adapt it. ATR based stops (in your case an ATR with a single period) are, in my opinion, the only real way to calculate stops:

/***
* GetUnits
* ========
* Parameters: |
* dblATR - The ATR upon which to base the calculation |
* dblStopLossMultiplier - the number of ATR's away from the entry price to use as a stop | |
* dblNominalCapital - the assumed amount of capital in US Dollars upon which to calculate a 1% maximum loss
*
* Returns: The number of units (lots) to trade that will only incur a maximum loss of 1% of capital if the order is stopped out |
*
* Description:
* When setting a specific stop-loss it is important to size a postion so that the loss does not exceed one percent of capital.
* This function uses the formula:
* Unit = 1% of Account divided by ATR * Dollars Per Point
*
* Example:
* We have $100,000 of capital and are prepared to risk 2% of this on each order. Our strategy places stops at 2.0 * ATR from the entry price.
*
* dblUnits = GetUnits( dblATR, 2.0, 100000, 2); // Returns number of lots to trade.
*
*/
double GetUnits( double dblATR, double dblStopLossMultiplier, double dblNominalCapital, double dblRiskPercent )
{
ErrorPush( "GetUnits");
double dblUnit, dblDollarsPerPoint, dblRiskOnOneContract, dblValueOfOneContract ;
int intMaxLots;
// On EURUSD this returns $1 for a 5-digit broker and $10 for a 4-digit broker as it is per point and not per pip (pip widely accepted as $.0001
dblDollarsPerPoint = MarketInfo(Symbol(),MODE_TICKVALUE) ;
// For EURUSD this returns a $100,000 contract size but by not hard-coding it we should get resilience for other currency pairs too
dblValueOfOneContract = dblDollarsPerPoint * MathPow(10,Digits);
// Now we calculate the risk if a gATR * dblStopLossMultiplier stop was applied to find the real risk in a stop-out situation
dblRiskOnOneContract = dblValueOfOneContract * dblATR * dblStopLossMultiplier;
// So now we know what could potentially be lost on one contract we size contracts to one per cent of our capital.
dblUnit = ((dblRiskPercent/100)*dblNominalCapital)/dblRiskOnOneContract;
// And because you can only trade in tenths of a contract with some brokers (mini lots) lets not support micro lots and round to one decimal place
dblUnit = NormalizeDouble( dblUnit, 1 );
// We return how many lots it is safe to trade for the current ATR, ATR Multiplier, current capital and % of capital we want to risk


/*******************************************************************************
* BROKER DEPENDENT RULES - DO THE LOTS HAVE TO BE ADJUSTED? *
* *
* If the proposed update breaks the broker's rules we have to adjust them *
*******************************************************************************
* These may differ from broker to broker
*/

//First define the rules

if ( StringFind(AccountCompany(), "OANDA")!=-1 || StringFind(AccountCompany(), "Oanda")!=-1 || StringFind(AccountCompany(), "oanda")!=-1 )
{
intMaxLots = 100;
}

if ( StringFind(AccountCompany(), "FXCM")!=-1 || StringFind(AccountCompany(), "fxcm")!=-1 )
{
intMaxLots = 100;
}

if ( StringFind(AccountCompany(), "Forex.com")!=-1 || StringFind(AccountCompany(), "forex.com")!=-1 )
{
intMaxLots = 50;
}

if (dblUnit > intMaxLots)
{
dblUnit = intMaxLots;
}

ErrorPop();
return (dblUnit);
}

Hope you find this useful.

Medran
PS Comment out the ErrorPush and ErrorPop - they are part of my debug system.

I'm not a programmer, so I didn't understand the variables that you've posted. Does it open trades with SL based on ATR? My SL is little tighter than ATR. But anywayz thanks. I hope someone would alter your codes to my needs. But I've found alot of people were looking the same thing.