How do i get the "day of Week" of the First of the Month?

[Bayne]

See above. I would bei grateful for an answer

[Benjamin Theriault]

int dayofweek;
MqlDateTime date;
datetime time = iTime(Symbol(), PERIOD_CURRENT, 0);
TimeToStruct(time, date);
if(date.day == 1){
        dayofweek = date.day_of_week;
}

Something like this, all depending of how you want to use it of course.

day_of_week = (0-Sunday, 1-Monday, ... 6-Saturday)

[William Roeder]

#property strict
#define  HR2400 (PERIOD_D1 * 60) // 86400 = 24 * 3600 = 1440 * 60
:
   datetime now = TimeCurrent();               // April 7, 2019 Sunday(0)
   int      dom = TimeDay(now);                // 7
   datetime first = now - HR2400 * (dom - 1);  // April 1, 2019 Monday(1)
   int      firstDay = TimeDay(first);         // 1

Find today. Subtract to the first. Find that day.

[paul selvan]

for any month :

int month_bar = 0;
int dayOfWeek = TimeDayOfWeek(iTime(_Symbol, PERIOD_MN1, month_bar));

[William Roeder]

paul selvan: for any month :

On MT4: Unless the current chart is that specific pair/TF referenced, you must handle 4066/4073 errors before accessing prices.
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On MT5: Unless the chart is that specific pair/TF, you must Synchronize the terminal Data from the Server.
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[paul selvan]

the number of monthly bar is limited as :

int max_monthly_bar= iBars(_Symbol,PERIOD_MN1)-1;

[Pimpinela]

Print("First day on current month is: ",TimeDayOfWeek(datetime(TimeYear(TimeCurrent())+"."+TimeMonth(TimeCurrent())+".1"))," Remember: (0 means Sunday,1,2,3,4,5,6)");

[Alessandro Pungitore]

here is a replacement function from mql4 for mql5:

//+------------------------------------------------------------------+
int TimeDayOfWeek(datetime pDate)
  {
   MqlDateTime date;
   TimeToStruct(pDate, date);
   return date.day;
  }
//+------------------------------------------------------------------+