2. simple expert advisor - mq4

8/10/2019 2. Simple Expert Advisor - MQ4

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Simple Expert Advisor

This section dwells on the principles of creating a simple trading Expert Advisor.

Problem 29. Create a trading Expert Advisor.

Preliminary Arguments

Before starting to program a trading Expert Advisor, it is necessar to define general

principles of a f!t!re program. There are no strict program creating r!les. "owever, once

having created a program, a programmer !s!all contin!es to improve it. To be able to easil!nderstand the program in f!t!re, it m!st be created in accordance with a well#tho!ght and

eas#to#!nderstand scheme $it is especiall important if a program will be f!rther improved b

another programmer%. The most convenient program is the one that consists of f!nctional

bloc&s, each of which is responsible for its part of calc!lations. To create an algorithm of a

trading Expert Advisor, let's anal(e what an operating program sho!ld do.

)ne of the most important data in the formation of trade orders is the information abo!t

orders that alread exist in a client terminal. *ome of trading strategies allow onl one

!nidirectional order. +enerall, if a trading strateg allows, several orders can be open in a

terminal at the same time, tho!gh their n!mber sho!ld be reasonabl limited. hen !sing an

strateg, trade decisions sho!ld be made ta&ing into acco!nt the c!rrent sit!ation. Before a

trade decision is made in a program, it is necessar to &now what trading orders have alread

been opened or placed. -irst of all a program m!st contain a bloc& of orders acco!nting which

is among the first to be exec!ted.

!ring an EA exec!tion trading decisions sho!ld be made, the implementation of which leads

to the exec!tion of trade operations. Code part responsible for trade orders formation is better

written in a separate bloc&. An Expert Advisor can form a trade re/!est to open a new pending

or mar&et order, close or modif an of existing orders or perform no actions at all. An EA

m!st also calc!late order prices depending on a !ser's desire.

Trade decisions sho!ld be made in a program on the bases of trade criteria. The s!ccess of the

whole program depends on the correctness of detecting trade criteria in the program. hen

calc!lating trade criteria a program can $and m!st% ta&e into acco!nt all information that can

be !sef!l. -or example, an Expert Advisor can anal(e combination of technical indicator

val!es, time of important news releases, c!rrent time, val!es of some price levels, etc. -or

convenience, the program part responsible for the calc!lation of trading criteria sho!ld be

written in a separate bloc&.

A trading Expert Advisor m!st necessaril contain error processing bloc&. Anal(ing errors

that ma occ!r in the exec!tion of trade operation allows, on the one side, to repeat a trade

re/!est and, on the other hand, to inform a !ser abo!t a possible conflict sit!ation.


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Structure of a Simple Expert Advisor

Below is a str!ct!ral scheme of a simple Expert Advisor constr!cted on the basis of several

f!nctional bloc&s, in each bloc& a certain detached part of calc!lations.

-ig. 019. *tr!ct!ral scheme of a simple Expert Advisor.

)n the following EA development stage there is no program code et. At the same time the

algorithm of a program is to a great extent formed. "ow the EA b!ilt on the bases of the

offered scheme will operate can be easil !nderstood simpl loo&ing on the scheme and

orienting !pon bloc& names and relations arras $control passing% between them.

After program start control is passed to the bloc& of preliminar processing. n this bloc&some general parameters can be anal(ed. -or example, if there are not eno!gh bars in a


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window $bars necessar for calc!lating parameters of technical indicators%, an EA will not be

able to operate ade/!atel. n s!ch a case an EA m!st terminate operation preliminaril

informing a !ser abo!t it and reporting abo!t the reason of termination. f there are no

contraindicatons of a general character, control is passed to order acco!nting bloc&.

n the bloc& of acco!nting orders the n!mber and /!alit of orders existing in a client terminalfor a sec!rit $to the window of which the EA is attached% is detected. n this bloc& orders of

other sec!rities m!st be eliminated. f a programmed trading strateg re/!ires !sing onl

mar&et orders $and does not !se pending orders% the fact of presence of pending orders m!st

be detected. f a strateg admits onl one mar&et order and there are act!all several orders,

this fact sho!ld also be &nown. The tas& of the order acco!nting bloc& $in this scheme% is in

defining whether the c!rrent trading sit!ation corresponds with an expected one, i.e. that in

which the EA can ade/!atel operate. f the sit!ation corresponds, control m!st be passed to

the next bloc& to contin!e the EA's operation3 if not, the EA's operation m!st be terminated

and this fact m!st be reported to a !ser.

f there are no orders in the terminal or the n!mber and /!alit of existing orders correspondsto what was expected, control is passed to the bloc& of defining trading criteria. n this bloc&

all criteria necessar for ma&ing trade decisions are calc!lated, namel criteria for opening,

closing and modifing orders. -!rther control is passed to the bloc& of closing orders.

t is eas to !nderstand wh in the offered scheme the bloc& of closing orders is exec!ted

earlier than the bloc& of opening orders. t is alwas more reasonable to process first existing

orders $close or modif% and onl after that to open new orders. +enerall, it is correct to be

g!ided b the desire to have as little orders as possible. !ring the exec!tion of this bloc& all

orders, for which the closing criterion has been activated, m!st be closed.

After all necessar orders has been closed, control is passed to a bloc& of new orders si(e

calc!lation. There are a lot of algorithms for calc!lating an order vol!me. The simplest of

them is !sing a constant, fixed lot si(e. t is convenient to !se this algorithm in a program for

testing strategies. 4ore pop!lar method of defining an order si(e is setting the n!mber of lots

depending on the amo!nt of free margin, for example 51#617 of it. f free margin is not

eno!gh, the program terminates its operation having informed a !ser abo!t the reason.

After the n!mber of lots for opening new orders is defined, control is passed to order opening

bloc&. f an of criteria calc!lated earlier points to the necessit of opening an order of a

certain tpe, a trade re/!est to open an order is formed in this bloc&.

There is also error anal(ing bloc& in an Expert Advisor. f an trade operation failed, control

$onl in this case% is passed to the error processing bloc&. f an error ret!rned b a server or

client terminal is not cr!cial, one more attempt is made to perform a trade operation. f a

cr!cial error is ret!rned $for example, an acco!nt is bloc&ed%, an EA m!st terminate its

operation. 8emember, in 4:6 there is no possibilit of program terminating an EA's

operation in a sec!rit window $as distinct from scripts, see *pecial -!nctions%. hat can be

done in a program wa is the termination of start$%. At a new start of the f!nction start$% on a

new tic& the val!e of a certain variable#flag prohibiting trading $in this case enabled as a

res!lt of a critical error% can be anal(ed and control can be passed for the termination of the

special f!nction operation3 th!s formation of new trade re/!est is not permitted. n the offered

scheme the flag val!e is anal(ed in the bloc& of preliminar processing.
http://book.mql4.com/programm/specialhttp://book.mql4.com/programm/special


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Trading Strategy

4ar&et prices are constantl moving. 4ar&et state at an moment of time can be conditionall

characteri(ed either as a trend # strong !nidirectional price change $rise or fall%, or as a flat #

lateral price movement with wea& deviations from a certain average. These mar&et

characteristics are conditional, beca!se there are no clear criteria, according to which trend or

flat can be identified. -or example, long lateral movements with strong deviations that can be

traced neither to a flat nor to a trend. +enerall it is ass!med that the mar&et is mainl in the

state of lateral movement and trends !s!all ta&e place 0;#217 of time.

-ig. 001. -lat and trend in the mar&et.

All trading strategies also can be conventionall divided into two main gro!ps. The first gro!p

contains flat#oriented strategies. The main idea of s!ch strategies is that after an evident

deviation price m!st ret!rn to the previo!s position, that's wh orders are opened in the

direction contrar to the last price movement. The second gro!p strategies are trend strategies,

when orders are opened in the same direction as the salt price movement. There are more

complicated $combined% strategies. *!ch strategies ta&e into acco!nt man different factors

that characteri(e mar&et3 as a res!lt trading can be exec!ted both on flat and trend. t is nothard to implement trading according to this or that strateg technicall # 4:6 contains all

necessar means for it. The main wor& in the creation of once own strateg consists in the

search of trading criteria.

Trading Criteria

n this example we will tr to constr!ct a trend Expert Advisor, i.e. the one that will open

orders in the price movement direction. *o, we need to find among vario!s technical

indicators those that detect a trend beginning. )ne of the simplest methods of searching

trading criteria is based on the analsis of the combination of 4As with different averaging


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periods. -ig. 000 and -ig. 002 show the position of two different 4A $with periods of

averaging 00 and 50% on different mar&et parts. Averages with small averaging period $red

lines% are closer to a price chart, twist and movable. 4oving averages with larger period of

averaging $bl!e line% are more inert, have larger lag and are sit!ated farther from mar&et

prices. :et's pa attention to places where 4As with different averaging periods cross and tr

to decide, whether the fact of 4A crossing can be !sed as a reading criterion.

-ig. 000. Crossing of 4A$00% and 4A$50% when price movement direction changes.

n -ig. 000 we see a mar&et part where opening orders in the direction of price movement at

4A crossing is

after that the mar&et price contin!es growing for some time. -!rther reverse 4A crossing

indicates the price movement direction change. f we open a B! order at point A and close it

at B, we will get profit proportional to difference of A and B prices.


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-ig. 002. Crossing of 4A$00% and 4A$50% when price movement direction changes.

At the same time there are other moments in the mar&et when 4A cross, b!t this does not lead

to f!rther considerable price rise or fall $-ig. 002%. )rders opened at 4A crossing at s!ch

moments will lead to losses. f *ell is opened at A and closed at B, s!ch trading will bring

losses. The same can be said abo!t a B! order opened at B and closed at C.

The s!ccess of the whole strateg implemented on the basis of 4A crossing depends on the

n!mber of parts that can be characteri(ed as trend and flat. n flat often 4A crossing is a

reg!lar event that interferes with an trend strateg. =!mero!s false signals as a r!le lead to

losses. That is wh this sign # crossing of 4As with different averaging period # can be !sedfor b!ilding trading strategies onl in combination with other signs proving a trend. n this

example $for constr!cting a simple Expert Advisor% we will have to ref!se !sing this sign.

e will !se another sign. Anal(ing vis!all the character of price changes in the mar&et, we

can see that a long one#direction price rise or fall often appears as a res!lt of a short strong

movement. n other words, if within a short period a strong movement happened, we ma

expect its contin!ation in a medi!m#term period.


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-ig. 005. *trong price movement can lead to a trend development.

-ig. 005 shows the mar&et period when a strong movement res!lted in the contin!ation of the

price change in the same direction. As the >a strong movement> we ma !se the difference of

4As with different averaging periods. The stronger the movement, the larger is the lag of 4A

with larger averaging period from 4A with a small period of averaging. 4oreover, even

strong discontin!o!s price movements with f!rther ret!rn do not res!lt in a large difference

between 4As, i.e. n!mero!s false signals do not appear. -or example, price

points with f!rther ret!rn $in the center in -ig. 005% entailed increase of difference between

4As onl b 21 points. At the same time a reall strong movement $which is not !s!all

accompanied b a considerable correction% in point A res!lted in the difference increase !p to2; # 51 points.

f B! order is opened when a certain val!e of difference between 4As is reached, for

example in A, most probabl the order will be profitable when a price reaches a preset *top

order val!e. :et's !se this val!e as a trading criterion in o!r Expert Advisor.

Number of Orders

n this example we anal(e an Expert Advisor that admits presence of onl one mar&et order,

pending orders are not provided. *!ch an approach is

example, b!t can be !sed as the basis for an strateg.

Pending orders are !s!all !sed when a developer has /!ite a reliable criterion for forecasting

the f!t!re price change with high probabilit. f there is no s!ch criterion, no need to !se

pending orders.

The sit!ation when several opposite orders for one sec!rit are open also cannot be

considered reasonable. t was written earlier that from economical point of view opposite

orders are considered to be senseless, especiall if the order prices are e/!al $see Closing and
http://book.mql4.com/trading/orderclosehttp://book.mql4.com/trading/orderclose


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eleting )rders%. n s!ch a case we sho!ld close one order b another one and wait for a

signal to open one mar&et order in a certain direction.

Relation of Trading Criteria

-rom this position it becomes clear what relations are possible between trading criteria. -ig.

006 shows three variants of correlation of trading criteria, when each criterion is important

$valid%. Actions $opening and closing mar&et orders% ta&e place cloc&wise on the following

pict!res.

-ig. 006. )rder opening and closing criteria correlation $a and b # correct, c # incorrect%.

The most pop!lar variant of a correctl formed trading criteria is the variant a. After being

opened a mar&et order B! is held !pon till the moment when criterion re/!iring its closing

triggers. After that a pa!se occ!rs when no orders are opened. -!rther a mar&et order *ell can

be opened. Conditions for closing a *ell order $in accordance with correctl formed criteria%

occ!r earlier, than conditions for opening a B! order. "owever, a B! order can be opened

once again, if a trading criterion re/!ires this. B!t according to this variant a mar&et order

cannot be opened if there is an open mar&et order in the contrar direction.

*imilar criteria correlation is in the variant b. The difference is that a criterion for opening anmar&et order is at the same time a criterion for closing the opposite order. This variant li&e the

variant adoes not allow several orders opened in the terminal at the same time on one

sec!rit.

The variant of criteria correlation is incorrect. According to this variant opening of a mar&et

order is allowed when contrar orders are not closed et, which is senseless. There can be rare

cases when this variant is partiall

acceptable for compensating losses occ!rring at small corrections after strong price

movements. n s!ch cases an opposite order can be opened of the same or smaller val!e than

the alread existing one and then closed when the correction is over. *!ch a tactic allows not

to interfere with the >main> order opened in the trend direction.
http://book.mql4.com/trading/orderclosehttp://book.mql4.com/trading/orderclose


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n general case several one#direction orders are also possible. This ma be

earlier opened order is protected b a *top order and the criterion pointing at the price

development in the same direction triggered once again. "owever, when creating s!ch a

strateg, a developer m!st be f!ll aware that in case of a sharp price movement change the

placed stop orders ma be !nexec!ted b some bro&ers at the first price to!ch. And the loss

will be proportionate to the total val!e of one#directional mar&et orders.

n o!r example we !se variant bof trading criteria correlation. All opened mar&et orders are

closed either b a stop order or after a criterion of opening an order in opposite direction

triggers $here criterion of closing B! coincides with that of opening *ell and vice versa%.

Size of Opened Orders

n an trading strateg order si(es sho!ld be reasonabl limited. n a simple case a fixed ordersi(e is !sed in an Expert Advisor. Before EA operation start, a !ser can set an si(e of f!t!re

orders and leave it !nchanged for some time. -!rther if balance changes, a !ser can set !p a

new val!e of lot n!mbers of opened orders.

A too small order si(e provides more confidence in operation at the !npredictable mar&et

change, b!t the profit in case of s!ccess will be not so large. f the order si(e is too large, large

profit can be ac/!ired, b!t s!ch an EA will be too ris&. ?s!all the si(e of opened orders is

set !p so, that margin re/!irements do not exceed 2#5;7 percent of the balance or free margin

$if a strateg allows onl one opened order, balance and free margin at the moment before the

order opening will be e/!al%.

n this example both variants are implemented. A !ser ma choose either to indicate directl

val!es of orders or set the val!e in percentage from the free margin.

Programming etails

A simple trend Expert Advisortradingexpert.m/6constr!cted on the basis of previo!s

arg!ments can loo& li&e this@

//--------------------------------------------------------------------// tradingexpert.mq4// The code should be used for educational purpose only.//--------------------------------------------------------------------#property copyright "Copyright oo! $$%"#property lin! "http&//'uto(raf.dp.ua"//--------------------------------------------------------------- ) -- // *umeric +alues for ,)extern double toposs 0$$1 // for an opened orderextern double Ta!e2rofit 031 // 56 for an opened orderextern int 2eriod7,'7)0))1 // 2eriod of ,' )extern int 2eriod7,'703)1 // 2eriod of ,'

extern double 8ast+or 09.$1 // :istance bet;een ,'sextern double ots 0$.)1 // trictly set amount of lotsextern double 2rots 0$.$%1 // 2ercent of free margin
http://book.mql4.com/c/book/mq4/experts/tradingexpert.mq4http://book.mql4.com/c/book/mq4/experts/tradingexpert.mq4http://book.mql4.com/c/book/mq4/experts/tradingexpert.mq4


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bool 0$0)?

Tic!et1 // Arder number double ,'7)7t // Current ,'7) +alue ,'77t // Current ,'7 +alue

ot // 'mount of lots in a selected order ts // 'mount of lots in an opened order ,in7ot // ,inimal amount of lots tep // tep of lot siBe change ree // Current free margin Ane7ot // 2rice of one lot

2rice // 2rice of a selected order // of a selected order T21 // T2 DE a selected order bool 'ns 0false // er+er response after closing Cls70false // Criterion for closing uy Cls70false // Criterion for closing ell Apn70false // Criterion for opening uy Apn70false1 // Criterion for opening ell//--------------------------------------------------------------- 3 -- // 2reliminary processing if>ars F 2eriod7,'7? // *ot enough bars @ 'lert>"*ot enough bars in the ;indo;. =' doesnGt ;or!."?1 return1 // =xit start>? H if>"e+eral mar!et orders. =' doesnGt ;or!."?1 return1 // =xit start>?

H Tic!et0ArderTic!et>?1 // *umber of selected order


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Tip 0ArderType>?1 // Type of selected order 2rice 0ArderApen2rice>?1 // 2rice of selected order 0Ardertoposs>?1 // of selected order T2 0ArderTa!e2rofit>?1 // T2 of selected order ot 0Arderots>?1 // 'mount of lots H

H//--------------------------------------------------------------- -- // Trading criteria ,'7)7t0i,'>*N$2eriod7,'7)$,A:=7*N$2eriod7,'7$,A:=7,'7)7t I ,'77t J 8ast+orQ2oint? // Lf difference bet;een @ // ..,' ) and is large Apn70true1 // Criterion for openinguy Cls70true1 // Criterion for closingell H

if >,'7)7t I ,'77t - 8ast+orQ2oint? // Lf difference bet;een @ // ..,' ) and is large Apn70true1 // Criterion for openingell Cls70true1 // Criterion for closinguy H//--------------------------------------------------------------- R -- // Closing orders ;hile>true? // oop of closing orders @ if >Tip00$ SS Cls700true? // Arder uy is opened.. @ // and there is criterionto close 'lert>"'ttempt to close uy "Tic!et". Tic!etot's!?1 // Closing ell if >'ns00true? // uccess &? @ 'lert >"Closed order ell "Tic!et?1 brea!1 // =xit closing loop H if >un7=rror>(etast=rror>??00)? // 2rocessing errors continue1 // 8etrying

return1 // =xit start>? H


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brea!1 // =xit ;hile H//--------------------------------------------------------------- % -- // Arder +alue 8efresh8ates>?1 // 8efresh rates ,in7ot0,ar!etLnfo>ymb,A:=7,L*AT?1 // ,inimal number of lots

ree 0'ccountree,argin>?1 // ree margin Ane7ot0,ar!etLnfo>ymb,A:=7,'8(L*8=NL8=:?1// 2rice of ) lot tep 0,ar!etLnfo>ymb,A:=7ATT=2?1 // tep is changed

if >ots F $? // Lf lots are set ts 0ots1 // ;or! ;ith them else // U of free margin ts0,athloor>reeQ2rots/Ane7ot/tep?Qtep1// or opening

if>ts I ,in7ot? ts0,in7ot1 // *ot less than minimal if >tsQAne7ot I ree? // ot larger than freemargin @

'lert>" *ot enough money for " ts" lots"?1 return1 // =xit start>? H//--------------------------------------------------------------- 9 -- // Apening orders ;hile>true? // Arders closing loop @ if >Total00$ SS Apn700true? // *o ne; orders J @ // criterion for openinguy 8efresh8ates>?1 // 8efresh rates 0id - *e;7top>toposs?Q2oint1 // Calculating of opened T20id J *e;7top>Ta!e2rofit?Q2oint1 // Calculating T2 of opened 'lert>"'ttempt to open uy. "Apened order ell "Tic!et?1 return1 // =xit start>? H if >un7=rror>(etast=rror>??00)? // 2rocessing errors continue1 // 8etrying return1 // =xit start>?

H brea!1 // =xit ;hile


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H//--------------------------------------------------------------- -- return1 // =xit start>? H//-------------------------------------------------------------- )$ --int un7=rror>int =rror? // unction of processing

errors @ s;itch>=rror? @ // *ot crucialerrors

case 4& 'lert>"Trade ser+er is busy. Trying once again.."?1 leep>3$$$?1 // imple solution return>)?1 // =xit the function case )3&'lert>"2rice changed. Trying once again.."?1 8efresh8ates>?1 // 8efresh rates return>)?1 // =xit the function case )3R&'lert>"*o prices. "Trading forbidden."?1 return>$?1 // =xit the function case )34&'lert>"*ot enough money to execute operation."?1 return>$?1 // =xit the function default& 'lert>"=rror occurred& "=rror?1 // Ather +ariants

return>$?1 // =xit the function H H//-------------------------------------------------------------- )) --int *e;7top>int 2arametr? // Chec!ing stop le+els @ int ,in7:ist0,ar!etLnfo>ymb,A:=7TA2=V=?1// ,inimal distance if >2arametr I ,in7:ist? // Lf less than allo;ed @ 2arametr0,in7:ist1 // ett allo;ed 'lert>"Lncreased distance of stop le+el."?1 H return>2arametr?1 // 8eturning +alue H//-------------------------------------------------------------- ) --

escribing !ariables


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)ne more criterion in program estimation is its readabilit. A program is considered to be

correctl written, if it can be easil read b other programmers, that's wh all main program

parts and main moments characteri(ing the strateg m!st be commented. This is also wh it is

recommended to declare and comment all variables at the beginning of the program.

n the bloc& 0#2 external and global variables are described.

According to r!les, external and global variables m!st be opened before their first !sage $see

Tpes of ariables%, that's wh the are declared in the program head part. All local variables

of the f!nction start$% are gathered and described in the !pper f!nction part $bloc& 2#5%

immediatel after the f!nction header. 8!les of declaring local variables do not re/!ire it, b!t

also do not prohibit. f a programmer faces diffic!lties in !nderstanding the meaning of a

variable when reading the program, he can refer to the !pper program part and find o!t the

meaning and tpe of an variable. t is ver convenient in programming practice.

"loc# of preliminary processing

n this example the preprocessing consists of two parts $bloc& 5#6%. The program terminates

operation if there are not eno!gh bars in a sec!rit window3 in s!ch a case it is impossible to

detect correctl $in bloc& ;#% val!es of moving averages necessar for calc!lating criteria.

Besides here the val!e of the variable or& is anal(ed. n the normal EA operation the

variable val!e is alwas 'tr!e' $it is set once d!ring initiali(ation%. f a critical error occ!rs in

the program operation, 'false' is assigned to this variable and start$% finishes its operation. This

val!e will not change in f!t!re, that is wh the following code is not exec!ted. n s!ch a case

the program operation m!st be stopped and the reason for the critical error m!st be detected$if needed, a dealing center m!st be contacted%. After the sit!ation is solved, the program can

be started once again, i.e. the EA can be attached to a sec!rit window.

Accounting orders

The described Expert Advisor allows wor&ing onl with one mar&et order. The tas& of the

orders acco!nting bloc& $bloc& 6#;% is to define characteristics of an opened order, if there is

one. n the loop going thro!gh orders 'for' all existing mar&et and pending orders are chec&ed,namel from the first $int i0% to the last one $iDlt3)rdersTotal$%%. n each ccle iteration the

next order is selected b the f!nction )rder*elect$%. The selection is made from a so!rce of

opened and pending orders $*E:ECTBFP)*%.

if >Arderelect>i-)==CT7K72A?00true? // Lf there is the next one

f the selection is exec!ted s!ccessf!ll $i.e. there is one more order in the terminal%, f!rther

this order and the sit!ation m!st be anal(ed@ whether the order is opened for the sec!rit, at

which the EA operates, whether the order is mar&et or pending3 it also m!st be ta&en into

acco!nt when co!nting orders. n the line@

if >Arderymbol>?M0ymb?continue1 // 'nother security
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all orders opened for another sec!rit are eliminated. )perator 'contin!e' stops the iteration

and characteristics of s!ch an order are not processed. B!t if the order is opened for the

sec!rit, to the window of which the EA is attached, it is f!rther anal(ed.

f )rderTpe$% ret!rns val!e more than 0 $seeTpes of Trades%, the selected order is a

pending one. B!t in this Expert Advisor managing pending orders is not provided. t meansthe exec!tion of start$% m!st be terminated, beca!se a conflict sit!ation occ!rred. n s!ch a

case after a message abo!t the operation termination start$% exec!tion is stopped b the

operator 'ret!rn'.

f the last chec& showed that the anal(ed order is a mar&et order, the total n!mber of orders

for a sec!rit is calc!lated and anal(ed. -or the first of s!ch orders all necessar

characteristics are defined. f in the next iteration the order co!nter $variable Total% finds the

second mar&et order, the sit!ation is also considered to be conflict, beca!se the EA cannot

manage more than one mar&et order. n s!ch a case start$% exec!tion is stopped after showing

a corresponding message.

As a res!lt of the order acco!nting bloc& exec!tion $if all chec&s were s!ccessf!l% the variable

Total preserves its (ero val!e if there are no mar&et orders, or gets the val!e 0 if there is a

mar&et order for o!r sec!rit. n the latter case some variables set in correspondence with the

order characteristics $n!mber, tpe, opening price, stop levels and order val!e% also get their

val!es.

Calculating Trading Criteria

n the anal(ed example definition of trading criteria $bloc& ;#% is calc!lated on the bases of

difference between 4oving Averages with different periods of averaging. According to

accepted criteria a chart is b!ll#directed if the c!rrent val!e of the 4A with smaller period is

larger than the val!e of 4A with larger period, and the difference between the val!es is larger

than a certain val!e. n a bear movement 4A with smaller period is lower than 4A with

larger period and the difference is also larger than a certain critical val!e.

At the bloc& beginning val!es of 4As with averaging periods Period4A0 and

Period4A2 are calc!lated. The fact of significance of an trading criterion is expressed via

the val!e of a corresponding variable. ariables )pnB and )pn* denote the criterion

triggering for opening B! and *ell orders, variables ClsG and Cls* # for closing. -orexample, if a criterion for opening B! has not triggered, the val!e of )pnB remains 'false'

$set at the variable initiali(ation%3 if it has triggered, )pnB gets the val!e 'tr!e'. n this case

the criterion for closing *ell coincides with that for opening B!, criterion for opening *ell

coincides with that for closing B!.

Trading criteria accepted in this example are !sed for ed!cational p!rpose onl

and m!st not be considered as a g!ideline when trading on a real acco!nt.

Closing Orders
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t was written earlier that this Expert Advisor is intended for operation onl with one mar&et

order opened for a sec!rit, to which window the EA is attached. To the moment when control

in the program is passed to the order closing bloc& it is &nown for s!re that at the c!rrent

moment there are either no orders for the sec!rit, or there is onl one mar&et order. That's

wh the code in orders closing bloc& is written so that onl one order can be closed

s!ccessf!ll.

This bloc& is based on the infinite loop 'while', the bod of which consists of two analogo!s

parts@ one for closing a B! order, another for closing a *ell order. 'hile' is !sed here for the

p!rpose that in case of a trade operation fail!re it co!ld be repeated once again.

n the header of the first operator 'if' condition for closing a B! order is calc!lated $*ell

orders are closed in the analogo!s wa%. f the tpe of an earlier opened order corresponds to

B! $see Tpes of Trades% and the sign for closing B! is relevant, control is passed to the

bod of 'if' operator where a re/!est to close is formed. As an order closing price in the

f!nction )rderClose$% the val!e of a two#sided /!ote corresponding to the order tpe is

indicated $see 8e/!irements and :imitations in 4a&ing Trades%. f a trade operation isexec!ted s!ccessf!ll, after a message abo!t the order closing is shown the c!rrent 'while'

iteration is stopped and the exec!tion of the order closing bloc& is over. B!t if the operation

fails, the !ser#defined f!nction for processing errors -!nError$% is called $bloc& 01#00%.

Processing Errors

As a passed parameter in -!nError$% the last error code calc!lated b +et:astError$% is !sed.

epending on the error code -!nError$% ret!rns 0 if the error is not critical and the operationcan be repeated, and 1 if the error is critical. Critical errors are divided into two tpes # those,

after which a program exec!tion can be contin!ed $for example, a common error% and those,

after which exec!tion of an trade operations m!st be stopped $for example, bloc&ed

acco!nt%.

if after an !ns!ccessf!l trade operation the !ser#defined f!nction ret!rns 0, the c!rrent 'while'

iteration is terminated and d!ring the next iteration another attempt is made to exec!te the

operation # to close the order. f the f!nction ret!rns 1, the c!rrent start$% exec!tion is stopped.

)n the next tic& start$% will be started b the client terminal again and if HIJK conditions for

order closing are preserved, another attempt to close the order will be made.

f d!ring error processing it is fo!nd o!t that f!rther program exec!tion is senseless $for

example the program operates on an old client terminal version% d!ring the next start the

exec!tion of the special f!nction start$% will be terminated in the bloc& of preliminar

processing when anal(ing the val!e of the variable or&.

Calculating Amount of $ots for Ne% Orders

Amo!nt of lots can be calc!lated in accordance with a !ser's settings following one of the twovariants. The first variant is a certain constant val!e set !p b a !ser. According to the second
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variant the amo!nt of lots is calc!lated on the basis of a s!m e/!al to a certain percentage $set

b a !ser% of a free margin.

At the beginning of the bloc& of defining the amo!nt of lots for new orders $bloc& L#M%

necessar val!es of some variables are calc!lated # minimal allowed amo!nt of lots and step

of lot change set !p b a bro&er, free margin and price of one lot for the sec!rit.

n this example the following is provided. f a !ser has set !p a certain non#(ero val!e of the

external variable :ts, for example 1.;, it is accepted as the amo!nt of lots :ts when a trade

re/!est to open an order is formed. f 1 is assigned to :ts, the n!mber of lots :ts is defined on

the basis of the variable Prots $percentage%, free margin and conditions set !p b a bro&er.

After :ts is calc!lated, a chec& is cond!cted. f this val!e is lower than the minimal allowed

val!e, the minimal allowed val!e is accepted. b!t if free margin is not eno!gh, after a

corresponding message the start$% exec!tion is terminated.

Opening Orders

The bloc& of opening orders $bloc& M#9% li&e the blo&e of opening orders is an infinite loop

'while'. n the header of the first operator 'if' conditions for opening a B! order are

calc!lated@ if there are no orders for the sec!rit $variable Total is e/!al to 1% and the sign for

opening a B! order is relevant $)pnB is tr!e %, control is passed to 'if' operator bod for

opening an order. n s!ch a case after rates are refreshed prices for stop levels are calc!lated.

al!es of stop levels are initiall set b a !ser in external variables *top:oss and Ta&eProfit.n a general case a !ser can set val!es for this parameters smaller that a bro&er allows.

Besides a bro&er ma change the minimal allowed distance at an moment $it is an often case

at strong mar&et movements, for example, before important news release%. That's wh before

each order opening stop levels m!st be calc!late ta&ing into acco!nt val!es set b! a !ser and

the minimal allowed val!e set !p b a bro&er.

-or calc!lating stop levels the !ser#defined f!nction =ew*top$% is !sed3 as a passed

parameter the stop level val!e set b a !ser is !sed. n =ew*top$% first the c!rrent minimal

allowed distance is calc!lated. f the val!e set b a !ser corresponds to a bro&er's

re/!irements, this val!e is ret!rned. f it is smaller than the allowed val!e, the val!e allowed

b a bro&er is !sed. Prices of stop re/!ests are calc!lated from the corresponding two#sided/!ote $see 8e/!irements and :imitations in 4a&ing Trades%.

A trade re/!est to open an order is formed !sing the f!nction )rder*end$%. -or the calc!lation

of order opening price and prices of stop re/!ests the two#sided /!ote val!es corresponding to

the order tpe are !sed. f a trade operation was s!ccessf!l $i.e. a server ret!rned the n!mber

of an opened order% after a message abo!t a s!ccessf!l order opening is shown. start$%

exec!tion is finished. f an order was not opened and the client terminal ret!rned an error, the

error is processed according to the algorithm described earlier.

Some Code Peculiarities
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The anal(ed Expert Advisor code is oriented to the implementation of a certain strateg.

=ote, some program lines contain variables and calc!lations that wo!ld be changed, if the

strateg were changed.

-or example, according to the accepted strateg the Expert Advisor is developed to wor& onl

with one order. This allowed to !se the variable Tic&et both for the identification of a closing

order n!mber $in bloc& of closing #L% and for the identification of a s!ccess of a trade

operation exec!tion when opening an order $in the bloc& of opening M#9%. n this case s!ch a

sol!tion is acceptable. "owever, if we ta&e the anal(ed code as the basis for the

implementation of another strateg $for example allow opposite orders% we will have to

introd!ce one or several variables to be able to recogni(e n!mbers of opened orders and

identif the s!ccess of trade operations.

n f!rther strateg modifications we will have to change come program lines containing part

of logics contained in the so!rce strateg. =amel in the order acco!nting bloc& we will nothave to terminate the program operation if there are several open orders for a sec!rit.

Besides, conditions for opening and closing orders will alslo change. This will entail the code

changing in bloc&s of opening and closing orders.

)n the basis of this analsis we can easil concl!de that the described simple Expert Advisor

is not perfect. n a general case, for the implementation of order acco!nting one sho!ld !se a

!niversal f!nction based on !sing data arras and not containing logics of a certain strateg.

The same can be said abo!t the bloc&s of opening and closing orders. A more complete

program m!st contain a main analtical f!nction, all other !ser#defined f!nctions m!st be

s!bordinate to it. This analtical f!nction m!st contain a program code, in which all

conditions for the implementation of an strateg are anal(ed3 all s!bordinate f!nctions m!st

perform limited actions. The f!nction of acco!nting orders m!st onl acco!nt orders,

f!nctions of opening and closing orders m!st onl open and close orders, and the analtical

f!nction m!st >thin&> and manage all other f!nctions, i.e. call them when needed.

2. simple expert advisor - mq4

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