Basic Scala for loop Issue - scala

Question

I am trying to learn scala, here I am using basic for loop, but I am getting errors while compiling.
object App {
def main(args: Array[String]) {
for (i <- 1 to 10; i % 2 == 0)
Console.println("Counting " + i)
}
}
Errors while compiling :
fortest.scala:5: error: '<-' expected but ')' found.
for (i <- 1 to 10; i % 2 == 0)
^
fortest.scala:7: error: illegal start of simple expression
}
^
two errors found
I am using scala version 2.9.1
Any idea what is the problem..............?

Answer 1

for (i <- 1 to 10 if i % 2 == 0)
println("Counting " + i)

Answer 2

Scala is not Java, thus you cannot use a regular Java syntax. Instead you have to do:
for{
i <- 1 to 10
if(i % 2 == 0)
}{println("Counting " + i)}
or with ; delimeters, inside the (,) parentheses:
for(i <- 1 to 10;if(i % 2 == 0)){
println("Counting " + i)
}
Also, note that Scala's for expressions, have some pretty nifty capabilities.
you can use a for expression with multiple "loop iterators" and conditions.
For instance, instead of writing:
for(i <- 1 to n; if(someCondition(i)){
for(j <- 1 to m; if(otherCondition(j)){
//Do something
}
}
You can simply write:
for{
i <- 1 to n
if(someCondition(i))
j <- 1 to m
if(otherCondition(j))
}{
//Do something
}
SIDE NOTE:
When you extend App (there's a trait of that name in Predef), you don't need to define a main method. You can simply write your code between the curly braces of object:
object MyClazz extends App {
for(i <- 1 to 10;if(i % 2 == 0)){
println("Counting " + i)
}
}

Answer 3

Take a look at the "by" method of the Range class to count by 2
object App {
def main(args: Array[String]) {
for (i <- 2 to 10 by 2)
Console.println("Counting " + i)
}
}
Or, like others have already stated you can fix your loop by doing
object App {
def main(args: Array[String]) {
for {
i <- 1 to 10
if i % 2 == 0
}
Console.println("Counting " + i)
}
}
Or another way:
object App {
def main(args: Array[String]) {
val evenNumbers = for {
i <- 1 to 10
if i % 2 == 0
} yield i
Console.println(evenNumbers.mkString("\n"))
}
}

Answer 4

The modulo 2 condition can be moved to an if clause.
object App {
def main(args: Array[String]) {
for (i <- 1 to 10)
if(i % 2 == 0)
Console.println("Counting " + i)
}
}

Answer 5

Here is the simply example;
for (i <- List(1, 2, 3) if i < 2) println(i)
The best way to exam your code is to use scala shell.

Answer 6

Basically, you are trying to use for-loop + iterator gaurd. Please find below syntax
for ( i <- 1 to 10 if (i%2==0) ) yield i