1 gentle introduction to programming tirgul 2: scala “hands on” in the lab

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Gentle Introduction to Programming

Tirgul 2: Scala “hands on” in the lab

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Today• Understanding compiler messages• Debugger• Self work - recursion• Home work

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Understanding Compiler MessagesOpen 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

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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?

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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

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Debugger – Add Breakpoint

• Right click on the desired line

• “Toggle Breakpoint”

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Debugger – Start Debugging

breakpoint

debug

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Debugger – Debug Perspective

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Debugger – Debugging

Current state

Current location

Back to Scala perspective

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Decimal Binary

• We want to print the binary representation of a decimal number

• Examples:• 0 -> 0• 8 -> 1000• 12 -> 1100• 31 -> 11111

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)

Example: d = 14

d Output at the end of stage Action at the end of stage

14 0 Insert 0 to left of output; divide d by 2

7 10 Insert 1 to left of output; divide d by 2 and round down

3 110 Insert 1 to left of output; divide d by 2 and round down

1 1110 Insert 1 to left of output; return.

Solution Dec2Bin.scala

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Exercise

• Write a function that simulates print on positive integers

• The function should print one digit at time• Example:

• printRec(1234) 1234

1 gentle introduction to programming tirgul 2: scala “hands on” in the lab

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