I really don't understand why this wont work...
for (int i = 1, int k = 2; i<=4000000; i++) {
}
While this will...
for (int i = 1; i<=4000000; i++) {
}
I need to initialize two variables but when I try the first code it wont compile, the code looks correct??
If you want to initialize multiple variables, then they need to be of the same type, and you have to use just one declaration, so it would look like this:
for (int i = 1, k = 2; i<=4000000; i++ ) {
}
I wrote a bit about the syntax of for loops in response to Types permitted in for loop variable declarations? This isn't quite the same question, but the answer makes sense here, too I think.
In general, you can have a look at the Java language specification for the for statement. You can declare and initialize any type of variable in a for loop, and can even declare multiple variables, so long as they're all the same type. The relevant productions in the grammar are:
BasicForStatement:
for ( ForInitopt ; Expressionopt ; ForUpdateopt ) Statement
ForInit:
StatementExpressionList
LocalVariableDeclaration
LocalVariableDeclaration:
VariableModifiersopt Type VariableDeclarators
VariableDeclarators:
VariableDeclarator
VariableDeclarators , VariableDeclarator
This means that you can do any of the following, e.g.,
for ( ; … ; … ) // no variable declaration at all
for ( int i; … ; … ) // variable declaration with no initial value
for ( int i=0; … ; … ) // variable declaration with initial value
for ( int i=0, j=1; … ; … ) // multiple variables
for ( final Iterator<T> it = …; … ; … ) // final variable
The fourth case is the one that you're concerned with at the moment.
As an aside, the ForInit can also be a StatementExpressionList, which means that instead of declaring and initializing variables, you can also just execute some statements. E.g, you could do this (but this isn't a particularly useful example):
for ( System.out.println( "beginning loop" ; … ; … )
Change as for (int i = 1, k = 2; i<=4000000; i++) {
From Doc
The general form of the for statement can be expressed as follows:
for (initialization; termination; increment) {
statement(s)
}
You can initialize as int i=1,k=2;
for (int i = 1, k = 2; i<=4000000; i++) {
2 consecutive initializations should be semi-colon separated like
int a; int b;
In the above case you've have separated them using a comma and so it gives a compilation error.
Regards.
if block - see the other answers. Somebody has flagged your answer as either 'not an answer', or 'very low quality', and I am reviewing that flag in a review queue. You are attempting to answer the question, so even though I think your answer is wrong, I won't recommend it is deleted in my role as a reviewer, because a downvote is the right course of action here.