Lot sizing risk based and also converting the currency of the account – expert for MetaTrader 4

So this is it, the following code is based on the following article https://www.fxtrademaker.com/fx_calculation.htm.
I had a lot of jobs where the customer was asking me to add a risk based lot sizing (so that when you loose a trade on a SL, you loose only this
particular percentage of your account, and not more based on the specific lot sizing), but I never knew the correct formula. Then I
discovered that you had 3 cases. (USD is going to be the main currency used)

    • First case is the “Direct Rate” if you look at the link above you will see it clearly explained. when you have a direct
      rate that means that for example your account is in USD and you have a currency like XXXUSD so the formula to
      calculate the lot size is the following : 
    //DIRECT RATES
    if(symbol_currency_right==acc_currency){// so when the right currency is the same as your account currency (XXXUSD) in our example
       lot_size=money_risk/(dix*sl);//then you divide the money that you want to risk by the Point digits times the size of the lot (standard,micro) times the pips of the SL
    }
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    • Second case is the “Indirect Rate“, it has a type USDXXX just look up the article to know how it is
      constructed, or analyse the code :
      else if(acc_currency==symbol_currency_left){//GBPXXX
         lot_size=money_risk*Ask/(dix*sl);
         }
      • Last and most complicated case is when the main currency (USD) is not in the symbol at all, you have to pass through a middle currency to
        convert it correctly so the type would be XXXXXX. The code is a bit more complicated, and an error that I had at the beginning was
        that the middle symbol wasn’t found in the market watch when you tried to get the current price, so first you have to add it
        else if(acc_currency!=symbol_currency_left&&acc_currency!=symbol_currency_right){///XXX XXX
           string symbol_2=StringConcatenate(symbol_currency_left,acc_currency);
           SymbolSelect(symbol_2,true);
           
           double r__2=SymbolInfoDouble(symbol_2,SYMBOL_ASK);
           
           if(r__2==0){
              symbol_2=StringConcatenate(acc_currency,symbol_currency_left);
              SymbolSelect(symbol_2,true);
              r__2=SymbolInfoDouble(symbol_2,SYMBOL_ASK);
              
              }
              
           lot_size=Ask*money_risk/(dix*sl*r__2);
           }

      This code will not work in the strategy tester unless you add a fixed quote of a middle symbol as entry.