can some body know about how to find the lowest and highest from x candles in the given period_D1?

use:

double val;
val=High[iHighest(NULL,0,MODE_HIGH,20,0)];

if you want it as an indicator, google HH_LL indicator, it will plot the highest and lowest of a moving average, you can modify it with the formula above if you want

Thanks for your response sir if i want to find highest and lowest of last 7 candles then

val=High[iHighest(NULL,PERIOD_D1,MODE_HIGH,7,0)];