An example of a multicurrency Expert Advisor that uses the loop, where each iteration is responsible for trading each symbol separately. 

In order not to depend on ticks of any of the symbols, the OnTimer function is used for event generation.

Values of Bollinger Bands are used for trading.

The EA trades according to the following strategy:

• Buy: the Ask price touches the bottom line of the Bollinger Bands calculated based on the low price.
  Close: the Bid price touches the bottom line of the Bollinger Bands, calculated based on the high price.
• Sell: the Bid price touches the upper line of the Bollinger Bands, calculated based on the high price.
  Close: the Ask price touches the upper line of the Bollinger Bands calculated based on the low price.
• Restrictions: only one deal can be conducted on one bar.

The presented code is only an example of how to create a multicurrency Expert Advisor. All the details of the program operation are described in the code.