How to accumulate and retain records in Buffer[] - in a MQL4 Custom Indicator? - buffer

Question

I am making a custom indicator, that displays the change in the closing price of a certain currency.
for ( i = limit; i >= 0; i-- ) {
totaleur = 0;
for ( x = i; x < i + 1; x++ ) {
totaleur = ( ( iClose( "EURUSD", 0, x )
- iClose( "EURUSD", 0, x - 1 )
)
/ iClose( "EURUSD", 0, x - 1 )
);
}
ExtMapBuffer1[i] = totaleur;
return(0);
}
in this case the indicator displays only the change in price of each observation.
Any ideas how to make it display the change in an observation plus all previous observations?

Answer 1

There are several important points to realise, so as to make the goal achieved:
1: do not prematurely escape in the first round, via return(0)
moving the command return(0); outside the code-execution block {...}from the forward-stepping ( i decreases ) for( i = limit ;...; i--){...} code-execution block will let the pointer step forward in (i),as the Custom Indicator uses a progressive, discontinuous, per-partes incremental ( in time ), evaluation ( ref. MQL4 documentation on Custom Indicator iCustom(...) calling interface parameters )
2: decide, whether the inner-loop ( a sum of fractions ) was correctly coded
the proposed expression providesa sum of N, per-Bar relative differences,nota sum of N absolute-differences, divided by a net price change over N bars.
While this might be working, the point is, whether the intended model is correct to sum relative differences ( percent change over different, variable individual bases ), or whether the sum ob absolute differences ought be only at the very end of the loop divided by a one, common, base -- the net price difference between the first and the last point ( over the N-bars base ), which is commonly a quantitative modelling practice when a noisy signal is subject to some cheap smoothing technique.
3: correct problems in accessing TimeSeries vectors ( negative index )
given the outer for ( i = limit; i >= 0; i-- ) loop permits the i to become zero,
given the inner for ( x = i; ... ) thus permits x == 0,
the x - 1 < 0 becomes a problem,
wherethe instruction iClose( _Symbol, PERIOD_CURRENT, x - 1 ) requests to access a value, that does not yet exist ( has a negative index into TimeSeries vector ).
for ( i = limit; // SET:_______________________ START at BAR[i == limit]
i >= 0; // PRE: PRE-CONDITION i >= 0
i-- // UPD: POST-UPDATE i-- STEP FORWARD IN TIME
) { // ___________________________________________________________
totaleur = 0; // ZEROISED
for ( x = i; // SET:_________________ START at BAR[x = (i)]
x < i + 1; // PRE: PRE-CONDITION x < (i)+1
x++ // UPD: POST-UPDATE x++ +1 STEP ( ONCE )
) { // _____________________________________________________
totaleur = ( ( iClose( "EURUSD", 0, x )
- iClose( "EURUSD", 0, x - 1 )
)
/ iClose( "EURUSD", 0, x - 1 )
);
} // LOOP KEPT STORING ANY INTERIM VALUE FOR EACH x INTO THE SAME <var>
ExtMapBuffer1[i] = totaleur;
return(0); //___________________________________DO NOT PREMATURELY RET/EXIT RIGHT FROM THE 1st LOOP
}
As you might have already noticed, the code permits just one loop in the inner for(){...}

Answer 2

If you need a sum of N previous observations - you need something like this:
for(i=limit; i>=0; i--) {
double totaleur = 0;
for(x=i; x<i+N; x++) {
totaleur += ((iClose("EURUSD", 0, x)- iClose("EURUSD", 0, x-1))/iClose("EURUSD", 0, x-1));
}
ExtMapBuffer1[i]=totaleur;
}
when you have return(0); inside loop - indicator will stop there and do not run that cycle with next parameter - so be careful with it