Array outside the OnTick function

hey guys, got a problem here: I want my EA to do a price level calculation exactly once per day and compare it to the prize level from the day before. I also want the time the calculation happens to be a user input, as well as it working on multiple timeframes. The way i am doing this is basically with the iHighest function, with the count being a variable. the variable is calculated by the Bars() function and datetime inputs, which are calculated by TimeCurrent, then just picking the year, month and day and string them together in a datetime string form. anyways, main issue right now is, i have to somehow access the datetime from 24 hours before the current datetime. i figured, this could be done by just storing the datetime in an array, and since the calculation is only done once per day you can just assign array[1]  =  array[0] at the end of the function. however, the array is reset every time the calculations are made, so the array[1] loses its value. taking the array out of the onTick function gives me multiple errors, mainly "array declaration without type", which i dont really understand. no compilation errors if i put it inside the onTick function though. any ideas? 

string timeArray[];

ArraySetAsSeries(timeArray,true);

ArrayResize(timeArray,2,0);



void OnTick(){

   int amountBars;

   MqlDateTime structTime;

   TimeCurrent(structTime);

   

   int intMonth = structTime.mon;

   string stringMonth;

   if(structTime.mon < 10){

      stringMonth = "0" + IntegerToString(intMonth);

   }

   if(structTime.mon >= 10){

      stringMonth = IntegerToString(intMonth);

   }

   

   

   int intDay = structTime.day;

   string stringDay;

   if(structTime.day < 10){

      stringDay = "0" + IntegerToString(intDay);

   }

   if(structTime.day >= 10){

      stringDay = IntegerToString(intDay);

   }

   

   



   

   string currentTimeDate = "D'"+IntegerToString(structTime.year)+"."+stringMonth+"."+stringDay;

   timeArray[0] = currentTimeDate;

   if(timeArray[0] != timeArray[1]){

      Print("NEW DAY");

   }

      Print(timeArray[1]," ",timeArray[0]);



   timeArray[1] = timeArray[0];

   string lookbackTimeDate;

  // amountBars = Bars(_Symbol,PERIOD_CURRENT,timeArray[1],timeArray[0]);

}