Cheat sheet

 A (65) - Z (90)

a (97) - z (122)

0 (48) - 9 (57)

enter - 13

space - 32

@ - 64

Who calls main()?   OS. 

Execution starts at main.

<< : output / put to / stream insertion operator

>> : input / get from / stream extraction operator

• calculation R to L
  
• 
  printing L to R