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# The predefined Variables
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For each executable mql5-program a set of predefined variables is supported, which reflect the state of the current price chart by the moment a mql5-program (Expert Advisor, script or custom indicator) is started.
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Values of predefined variables are set by the client terminal before a mql5-program is started. Predefined variables are constant and cannot be changed from a mql5-program. As exception, there is a special variable _LastError, which can be reset to 0 by the [ResetLastError](/en/docs/common/resetlasterror) function.
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| Variable | Value |
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| --- | --- |
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| _AppliedTo | The _AppliedTo variable allows finding out the type of data, used for indicator calculation |
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| _Digits | Number of decimal places |
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| _Point | Size of the current symbol point in the quote currency |
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| _LastError | The last error code |
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| _Period | Timeframe of the current chart |
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| _RandomSeed | Current status of the generator of pseudo-random integers |
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| _StopFlag | Program stop flag |
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| _Symbol | Symbol name of the current chart |
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| _UninitReason | Uninitialization reason code |
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| _IsX64 | The _IsX64 variable allows finding out the bit version of the terminal, in which an MQL5 application is running |
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Predefined variables cannot be defined in a library. A library uses such variables that are defined in program from which this library is called.
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# int _AppliedTo
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The _AppliedTo variable allows finding out the type of data, used for indicator calculation:
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| Data type | Meaning | Description of data used for indicator calculation. |
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| --- | --- | --- |
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| — | 0 | The indicator uses the second OnCalculate() call form - the data for calculation are not specified by a certain buffer or data array |
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| Close | 1 | Close prices |
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| Open | 2 | Open prices |
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| High | 3 | High prices |
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| Low | 4 | Low prices |
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| Median Price (HL/2) | 5 | Median price = (High+Low)/2 |
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| Typical Price (HLC/3) | 6 | Typical price = (High+Low+Close)/3 |
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| Weighted Price (HLCC/4) | 7 | Weighted price = (Open+High+Low+Close)/4 |
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| Previous Indicator's Data | 8 | Data of the indicator, which was launched on the chart before this indicator |
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| First Indicator's Data | 9 | Data of the indicator, which was launched first on the chart |
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| Indicator handle | 10+ | Data of the indicator, which was passed to the iCustom() function using the indicator handle. The _AppliedTo value contains the indicator handle |
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Example:
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```
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//+------------------------------------------------------------------+
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//| Custom indicator initialization function |
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//+------------------------------------------------------------------+
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int OnInit()
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{
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//--- indicator buffers mapping
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SetIndexBuffer(0,Label1Buffer,INDICATOR_DATA);
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// Getting the type of data used for indicator calculation
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Print("_AppliedTo=",_AppliedTo);
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Print(getIndicatorDataDescription(_AppliedTo));
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//---
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return(INIT_SUCCEEDED);
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}
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//+------------------------------------------------------------------+
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//| Description of data used for indicator calculation |
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//+------------------------------------------------------------------+
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string getIndicatorDataDescription(int data_id)
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{
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string descr="";
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switch(data_id)
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{
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case(0):descr="It's first type of OnCalculate() - no data buffer";
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break;
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case(1):descr="Indicator calculates on Close price";
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break;
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case(2):descr="Indicator calculates on Open price";
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break;
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case(3):descr="Indicator calculates on High price";
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break;
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case(4):descr="Indicator calculates on Low price";
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break;
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case(5):descr="Indicator calculates on Median Price (HL/2)";
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break;
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case(6):descr="Indicator calculates on Typical Price (HLC/3)";
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break;
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case(7):descr="Indicator calculates on Weighted Price (HLCC/4)";
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break;
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case(8):descr="Indicator calculates Previous Indicator's data";
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break;
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case(9):descr="Indicator calculates on First Indicator's data";
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break;
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default: descr="Indicator calculates on data of indicator with handle="+string(data_id);
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break;
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}
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//---
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return descr;
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}
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```
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See also
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[ENUM_APPLIED_PRICE](/en/docs/constants/indicatorconstants/prices#enum_applied_price_enum)
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# int _Digits
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The _Digits variable stores number of digits after a decimal point, which defines the price accuracy of the symbol of the current chart.
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You may also use the [Digits()](/en/docs/check/digits) function.
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# double _Point
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The _Point variable contains the point size of the current symbol in the quote currency.
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You may also use the [Point()](/en/docs/check/point) function.
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# int _LastError
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The _LastError variable contains code of the last [error](/en/docs/constants/errorswarnings/errorcodes), that occurred during the mql5-program run. Its value can be reset to zero by [ResetLastError()](/en/docs/common/resetlasterror).
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To obtain the code of the last error, you may also use the [GetLastError()](/en/docs/check/getlasterror) function.
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# ENUM_TIMEFRAMES _Period
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The _Period variable contains the value of the timeframe of the current chart.
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Also you may use the [Period()](/en/docs/check/period) function.
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See also
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[PeriodSeconds](/en/docs/common/periodseconds), [Chart timeframes](/en/docs/constants/chartconstants/enum_timeframes), [Date and Time](/en/docs/dateandtime), [Visibility of objects](/en/docs/constants/objectconstants/visible)
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# _RandomSeed
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Variable for storing the current state when generating pseudo-random integers. _RandomSeed changes its value when calling [MathRand()](/en/docs/math/mathrand). Use [MathSrand()](/en/docs/math/mathsrand) to set the required initial condition.
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x random number received by MathRand() function is calculated in the following way at each call:
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```
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x=_RandomSeed*214013+2531011;
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_RandomSeed=x;
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x=(x>>16)&0x7FFF;
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```
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See also
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[MathRand()](/en/docs/math/mathrand), [MathSrand()](/en/docs/math/mathsrand), [Integer types](/en/docs/basis/types/integer)
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# int _StopFlag
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The _StopFlag variable contains the mql5 program stop flag equal to 0 during normal operation. When the client terminal tries to stop the program, the variable is set to a value other than zero.
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To check the state of the _StopFlag you may also use the [IsStopped()](/en/docs/check/isstopped) function.
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# string _Symbol
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The _Symbol variable contains the symbol name of the current chart.
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You may also use the [Symbol()](/en/docs/check/symbol) function.
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# int _UninitReason
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The _UninitReason variable contains the code of the program [uninitialization reason](/en/docs/constants/namedconstants/uninit).
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Usually, this code is obtained by [UninitializeReason()](/en/docs/check/uninitializereason)the function.
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# int _IsX64
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The _IsX64 variable allows finding out the bit version of the terminal, in which an MQL5 application is running: _IsX64=0 for the 32-bit terminal and _IsX64!=0 for the 64-bit terminal.
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Also, function [TerminalInfoInteger(](/en/docs/check/terminalinfointeger)[TERMINAL_X64](/en/docs/check/terminalinfointeger)[)](/en/docs/check/terminalinfointeger) can be used.
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Example:
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```
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// Checking the terminal, in which the program is running
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Print("_IsX64=",_IsX64);
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if(_IsX64)
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Print("Program ",__FILE__," is running in the 64-bit terminal");
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else
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Print("Program ",__FILE__," is running in the 32-bit terminal");
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Print("TerminalInfoInteger(TERMINAL_X64)=",TerminalInfoInteger(TERMINAL_X64));
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```
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See also
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[MQLInfoInteger](/en/docs/check/mqlinfointeger), [Importing functions (#import)](/en/docs/basis/preprosessor/import)
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