Like printf, 0N! is your friend. When you place 0N! before an expression, it prints the result of that expression to the console and then returns it:

q)1 + 0N! til 10
0 1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10
q)

0N! does change the functionality of your code in one subtle, albeit usually harmless, way. If you place 0N! before a modifier-assignment operator (e.g. +:, -:), then the result of that assignment is no longer null; it is the value assigned:

q){x +: 47} 1
q){0N! x +: 47} 1
48
48
q)

See also: .Q.s and .Q.s1