1. 1 Gentle Introduction to Programming Tirgul 2: Scala “hands on” in the lab

2. 2 Today Understanding compiler messages Debugger Self work - recursion Home work

3. 3 Understanding Compiler Messages Open the interpreter, try the following lines of code, and try to understand what the compiler means, and how to solve it val x = 5 x = 6 Println(“123”) val f = (x : Int => x + 1) if x > f(x) x = 9 val f = (x : int) => x + 1

4. 4 And In Eclipse Select and copy a program of your choice to Eclipse How are compilation errors marked in Eclipse? Perform compilation errors purposely and see how the compiler’s errors look like: Change an upper-case letter to lower case Remove a closing brackets Where are the compiled files?

5. 5 Today Understanding compiler messages Debugger Self work - recursion Home work

6. 6 The Debugger Use the program you used earlier Set a break point and start following your program step by step Step in to a function and out from it Make sure you take a look at the program’s stack and variables’ state Here are the technical instructions

7. 7 Debugger – Add Breakpoint Right click on the desired line “Toggle Breakpoint”

8. 8 Debugger – Start Debugging breakpoint debug

9. 9 Debugger – Debug Perspective

10. 10 Debugger – Debugging Current state Current location Back to Scala perspective

11. 11 Today Understanding compiler messages Debugger Self work - recursion Home work

12. Decimal  Binary We want to print the binary representation of a decimal number Examples: 0 -> 0 8 -> 1000 12 -> 1100 31 -> 11111

13. Decimal  Binary Recursively The conversion of a number d from decimal to binary: If d is 0 or 1 – write d to the left and stop, else: If d is even, write ‘0’ to the left If d is odd, write ‘1’ to the left Repeat recursively with floor(d/2)

14. Example: d = 14 d Output at the end of stage Action at the end of stage 140 Insert 0 to left of output; divide d by 2 710 Insert 1 to left of output; divide d by 2 and round down 3110 Insert 1 to left of output; divide d by 2 and round down 11110 Insert 1 to left of output; return.

15. Solution Dec2Bin.scala

16. 16 Today Understanding compiler messages Debugger Self work - recursion Home work

17. Exercise Write a function that simulates print on positive integers The function should print one digit at time Example: printRec(1234)  1234