A file name is being passed down into a function. The string needs to be checked to make sure it ends with ".bmp" 

How do i check for that to later open the file?

**For example**: if a string contains "*picture.txt*" it will tell the user the string is not in the correct format. If a string contain "*picture.bmp*" it should accept it for later use of opening the file. 

Thanks in advance!