Get Highest and Lowest point between a time?

Yes, there is! Read the documentation for Access to Timeseries and Indicator Data, especially for the following functions:

• iHighest() & iHigh()
• iLowest() & iLow()
• iBarShift()

Of course there is. It always happens and that what makes it more complicated. When you are in for a long time, you can get used to it and try to generate some ideas and strategies.

Okay, thank you a lot!

And another question. Every currency Pair has diffrent amount of numbers. For example EUR/JPY ist xxx.xxx and EUR/USD is x.xxxxx ...
How can I write an EA for both currency pairs? - Or do I need for every currency pair another EA? 

No, you just need to adjust to the currency pair's tick size and number of digits. Do a search on the forum as there are plenty of threads and posts about that.

Ok, thank you. I found something about the digits, but not about the tick size... - what ist that?

There is also plenty of posts about Tick Size (MODE_TICKSIZE), especially in comparisons to Point Size (MODE_POINT) and also when used in conjunction with Tick Value (MODE_TICKVALUE). Read the documentation on this as well as search the forum.

There is Tick, PIP, and Point. They are all different in general. A tick is the smallest change of price. A Point is the least significant digit quoted. In currencies a pip is defined as 0.0001 (or for JPY 0.01)

On a 4 digit broker a point (0.0001) = pip (0.0001). [JPY 0.01 == 0.01] On a 5 digit broker a point (0.00001) = 1/10 pip (0.00010/10). Just because you quote an extra digit doesn't change the value of a pip. (0.0001 == 0.00010) EA's must adjust pips to points (for mq4.) In currencies a tick is a point. Price can change by least significant digit (1.23456 -> 1.23457)

In metals a Tick is still the smallest change but is larger than a point. If price can change from 123.25 to 123.50, you have a TickSize of 0.25 and a point of 0.01. Pip has no meaning.

This is why you don't use TickValue by itself. Only as a ratio with TickSize. See DeltaValuePerLot()