求编程高手帮忙刚学编程遇到个问题求教，先多谢了

我学习mql4编程时间不长，之前没有编程基础，在网上找了个《MQL4课程》学习之后对ea编程有了初步的了解，但遇到一个问题，教程中用来举例而编写了一个简单的指标，指标的全部代码是：

//+------------------------------------------------------------------+
//| 我的第一个指标.mq4 |
//| |
//| |
//+------------------------------------------------------------------+
#property copyright ""
#property link ""

#property indicator_separate_window
#property indicator_buffers 1
#property indicator_color1 Red
//---- buffers
double ExtMapBuffer1[];
//+------------------------------------------------------------------+
//| Custom indicator initialization function |
//+------------------------------------------------------------------+
int init()
{
//---- indicators
SetIndexStyle(0,DRAW_LINE);
SetIndexBuffer(0,ExtMapBuffer1);
string short_name = "我的第一个指标正在运行!";
IndicatorShortName(short_name);
//----
return(0);
}
//+------------------------------------------------------------------+
//| Custom indicator deinitialization function |
//+------------------------------------------------------------------+
int deinit()
{
//----

//----
return(0);
}
//+------------------------------------------------------------------+
//| Custom indicator iteration function |
//+------------------------------------------------------------------+
int start()
{
int counted_bars=IndicatorCounted();
//---- check for possible errors
if (counted_bars<0) return(-1);
//---- last counted bar will be recounted
if (counted_bars>0) counted_bars--;
int pos=Bars-counted_bars;
double dHigh , dLow , dResult;
Comment("嗨，在主窗口这儿!");
//---- main calculation loop
while(pos>=0)
{
dHigh = High[pos];
dLow = Low[pos];
dResult = dHigh - dLow;
ExtMapBuffer1[pos]= dResult ;
pos--;
}
//----
return(0);
}
//+------------------------------------------------------------------+

代码的意思我大体都懂，其中有两句代码
if (counted_bars>0) counted_bars--;和
int pos=Bars-counted_bars;

比如图表上有20根k线，第20根k线是正在跳动的k线，想恳请高手帮忙把例子中的值代入上面两句代码中

恳请高手帮忙，在此我先多谢了