How do I convert this for loop into a while loop? [closed]

Answer 1

int [] list = new int [5];

int i = 0; // initialization
while (i < 5) { // condition
    list [i] = i + 2;
    i++; // afterthought
}

The for loop posted is pretty much a shorthand for the above. The first part of a for loop is called the initialization, equivalent to the int i = 0; in the above code. The next is called the condition, which, if true, will cause the loop to be run again; this is the i < 5 part. Finally there is the afterthought, which changes the iterator i (usually an increment of one for iterating over an array). The for loop simply condenses these three parts into one line, as such:

for (initialization; condition; afterthought) {
}

Answer 2

The general structure of a basic for statement is:

for ( ForInit ; Expression ; ForUpdate ) Statement

• ForInit is the initializer. It is run first to set up variables etc.
• Expression is a boolean condition to check to see if Statement should be run
• Statement is the block of code to be run if Expression is true
• ForUpdate is run after the Statement to e.g. update variables as necessary

After ForUpdate has been run, Expression is evaluated again. If it is still true, Statement is executed again, then ForUpdate; repeat this until Expression is false.

You can restructure this as a while loop as follows:

ForInit;
while (Expression) {
  Statement;
  ForUpdate;
}

In order to apply this pattern to a "real" for loop, just substitute your blocks as described above.

For your example above:

• ForInit => int i = 0
• Expression => i < 5
• ForUpdate => i++
• Statement => list [i] = i + 2;

Putting it together:

int i = 0;
while (i < 5) {
  list[i] = i + 2;
  i++;
}

Answer 3

Your while loop is perfetly fine, but after it ends, the value of i is 5. Since java arrays are always indexed from zero, list[5] doesn't exist and accessing it throws exception.

That's what you see when printing System.out.print(list[i] + " "); Just print any other element, list[1], list[4] or list[0] for example.