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Variable assignment inside for loop [duplicate]

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This is a very simple for loop:
for(int i=0;i<=100;i++)
{
System.out.println(i);
}
I know how it mostly works, but I don't understand how the i++ works at the end: its supposed to add 1, if I'm correct, but when it prints out the i, it prints out 0 and then 1.
Why doesn't it just start out with 1 because of the i++? Why does it still just print out the original value instead of the i++ value?

A for loop works as follows:
Initialization is done (int i=0 in your case; only executed once)
Condition is checked (i<=100 here), if condition is false leave the loop
Code within the braces is executed (System.out.println(i); in your case)
Update statement is executed (i++)
Goto 2.

It's similar to this while loop :
{
int i = 0;
while (i <= 100) {
System.out.println(i);
i++;
}
}
i is incremented only at the end of each iteration.

Because the increment is evaluated after the first execution of the loop body. This is by design, and remember that programmers generally treat 0 as the first number. For example, with arrays and String(s) the first element is 0.
The Java Tutorial on The for Statement says,
The for statement provides a compact way to iterate over a range of values. Programmers often refer to it as the "for loop" because of the way in which it repeatedly loops until a particular condition is satisfied. The general form of the for statement can be expressed as follows:
for (initialization; termination; increment) {
statement(s)
}
When using this version of the for statement, keep in mind that:
The initialization expression initializes the loop; it's executed once, as the loop begins.
When the termination expression evaluates to false, the loop terminates.
The increment expression is invoked after each iteration through the loop; it is perfectly acceptable for this expression to increment or decrement a value.

Here it is how it works
The for statement is used to repeat a block of statements enclosed in curly braces. An increment counter is usually used to increment and terminate the loop. The for statement is useful for any repetitive operation, and is often used in combination with arrays to operate on collections of data/pins.
There are three parts to the for loop header:
for (initialization; condition; increment / decrement) {
//statement(s);
}
The initialization happens first and exactly once. Each time through the loop, the condition is tested; if it's true, the statement block, and the increment is executed, then the condition is tested again. When the condition becomes false, the loop ends.
Credits : For

If you use ++ operator as prefix like: ++var; then, the value of operand is increased by 1 then, only it is returned but, if you use ++ as postfix like: var++; then, the value of operand is returned first then, only it is increased by 1.
For example,
class Example
{
public static void main(String[] args)
{
int var = 1;
System.out.println(var++);
System.out.println("\n" + ++var);
}
}
the following program prints
1
3
In the prefix form, the increment or decrement takes place before the value is used in expression evaluation, so the value of the expression is different from the value of the operand. In the postfix form, the increment or decrement takes place after the value is used in expression evaluation, so the value of the expression is the same as the value of the operand.

Think of the i++ as the statement that says "Use then increment"
The value of i will first be used in the loop and then incremented by 1.
So the loop is executed once, then the declaration and incremental statements checked.

How to break continue a nested for-loop inside a while-loop?

Can I use break on a nested for-loop to get back to outer while-loop and use continue from inside the for-loop to force the while-loop to keep going? I can not get the for-loop conditions into my while-loop conditions so the while-loop might stop if I cannot continue on a specifically meet situation.
while(...some conditions...){
...print stuff
for(...some instances are arrays, condition loop array...){
if(...index meets conditions...){
...print once, some arrays might meet condition on multiple index
break; //to prevent multiple printings
}
continue; //i don't want to force another while iteration if(false)
//or is this continue for(loop) anyway?
}
continue; //is this not essentially a while(true) loop with no return?
}
The reason I can not get the for-loop conditions into the while conditions is because there are more if conditions between the two loops like if(array == null) and if-condition x == true getArray() needs to be called if array is not passed in. Most of the time condition y and z print from while-loop but sometimes condition x is met so I need the for-loop. It's after the printing of the for-loop if(index true)) I need the while-loop to go again that I'm stuck with? Sometime this might happen from while-loop conditions anyway but I can see that it wont always, further more if for-loop if(index false)) is meet I don't want to force the while loop as this could get costly in run time processing and could possibly result in an endless loop.
PS I am a junior programer, I'm not even sure it this is possible?
or makes sense, sorry if its a stupid question

you can name your loops like this:
namedLoop: for(...) {
// access your namedloop
break namedLoop;
}

You can break with label.
Here is a complete example showing it:
https://docs.oracle.com/javase/tutorial/displayCode.html?code=https://docs.oracle.com/javase/tutorial/java/nutsandbolts/examples/BreakWithLabelDemo.java
Basically the code is similar to this:
:myLabel
for (...) {
for(...) {
...
break myLabel; // Exit from both for loops
}
}

continue and break apply to the immediate current scope, so if you're inside the for, it will apply to the for.
You can store the comparison result on a boolean variable to check if you want to continue.
I'm not a big fan of break and continue, it hinders readability in my opinion. You can acheive the same behavior using a different code structuring.

Can a termination variable in a condition of for loop be changed inside the loop?(Java)

in Java, when using a for loop, you need to write a termination condition of course. This is my for loop:
for(int i=1; i<=infix.length()-2; i++){
if(infix.charAt(i)==' '){
infix=infix.substring(0,i)+infix.substring(i+1);
}
(infix is a string i got as a parameter). As you can see, I'm using substring inside the loop, which shortens the length of infix, which means that the termination condition of the loop is changed after every single iteration.
My question is this: Is the value "infix.length-2" saved at the beginning of the for and doesn't change later on? Or it changes every time, and if so, what happens with i? When will the for stop? Is there a chance for an index out of bounds or something like that?
Thank you very much in advance! :D

The string length gets calculated every loop, and your for could throw an IndexOutOfBoundsException if your string becomes too short.
IMHO yours is a very bad practice, for loops are intended to make a determined number of loops and should never be stopped, also their stop condition should never be changed inside the loop, you should use a while if you don't know how many iterations you want to do. But this is my personal opinion :)

Yes, you can change the upper limit. No, it's not cached at the beginning of the loop. Yes, anything you do wrong might cause errors -- but this is neither especially dangerous or uncommon. On the contrary, it's quite common.

you can put multiple end criteria in a for loop, just for a sample syntax
for(int i = 0; i < 2 || i< 5; i++)
System.out.println(i);

As a short hint: Your for-loop is equivalent to the following while-loop
{
int i=1;
while(i<=infix.length()-2) {
if(infix.charAt(i)==' '){
infix=infix.substring(0,i)+infix.substring(i+1);
}
i++
}
}
That means the condition of a the for-loop is evaluated in the same way as the condition of a while-loop. There is nothing special about it.

My question is this: Is the value "infix.length-2" saved at the beginning of the for and doesn't change later on? Or it changes every time, and if so, what happens with i?
It changes with every iteration of the for loop. i gets incremented, with each iteration.
When will the for stop? Is there a chance for an index out of bounds or something like that?
The for loop will stop when the termination condition is true.
i<=infix.length()-2.
i initialized to 1 will result in a loop that terminates if the length
If you modify the termination condition variables with incorrect logic, then you have a chance of running into an infinite loop.

nested while loops - outer vs inner conditions

In the example below does the inner while loop continue to execute it's statements 2 after the outer loop condition becomes false? Or once the outer while loop condition becomes false the ENTIRE loop exits including the inner while loop even though the condition for the inner while loop is true?
while (becomes false){
statements 1;
statements 1;
while ( true at the time the outer loop condition become false){
statements 2;
statements 2;
}
}
println("print something interesting");

It may help to understand how a while loop works. If you write:
while(myCondition) {
doSomething();
doSomethingElse();
}
println("print something interesting");
Then it basically becomes (in pseudo-code):
1. if myCondition continue to line 2, else go to line 5
2. doSomething()
3. doSomethingElse()
4. go to line 1
5. println "print something interesting"
As you can see, the condition is only checked at line 1. If myCondition becomes false during line 2, for instance, there's nothing to short-circuit the block. (If you need that, you have to manually re-test myCondition and call break if it's false.) This is true even if doSomething() is replaced by a while loop, for loop, or anything else.
So, if "statements 2" make the outer loop condition false, nothing will stop. The program will go on its merry way until the inner loop finishes, at which point the out loop finishes its iteration (since there's nothing after the inner loop within the outer loop's block) and goes back to re-test its condition to see if it should start another iteration. Only then does the outer loop check its condition.
To make it a tad more explicit, here's how your code basically works:
1. if outer-condition continue to line 2, else go to line 9
2. statements-1
3. statements-2
4. if inner-condition continue to line 5, else go to line 8
5. statements-2
6. statements-2
7. go to line 4
8. go to line 1
9. println "print something interesting"
So, outer-condition is only checked at line 1. If it becomes false at any point, the loop won't even notice until it gets to line 1, which will only happen once it gets to line 8 (or the first time it hits line 1 to start the while loop, of course).

the inner loop will only be executed (tested for condition) if the outer loop is true. otherwise if outer loop breaks, nested loop has no chance to get executed.

First of all, while loop conditions are only checked at the start of each iteration.
If, at the start of an outer loop iteration, the condition is false, contol is transferred the statement following the outer loop, thereby bypassing the inner loop.

Think of code in a code block (aka the curly brackets) as a door. If you do not meet the requirments to enter the door then you cant see anything inside. So no the inner loop (since the outer loop is false) will not execute.

Use a local variable for controlling the loop so you can check for this value in loop 2.

Giving name to a loop

While browsing questions and answers in this forum i found a piece of code were names were given to loops in order to use them for break. Like
nameofloop:
for(){
for(){
if(){ break nameofloop;}
}
}
Im new to programming and i havent seen that before. My question is what other uses of naming loops are there?

This is not a labeled loop, is just a label that you place anywhere and then you can "break" or "continue" to depending on your conditions. You can also use in a nested if-else with for loopings in order to break several loops decorated with if-else, so you can avoid setting lot of flags and testing them in the if-else in order to continue or not in this nested level.
Its use is discouraged as resembles a goto and causes spaghetti-code.
Personally I used only once, time ago, in order to break a for loop inside other two for loops with if-else and continue in the outer loop, as break inside a loop breaks this loop, but you continue in the outer loop, not the most-outer that was my case.

You can also say:
continue nameofloop;
...to jump to start of the named loop. I don't think there are any other use cases for labels in Java.

It's known as a labelled break which is a form of branching statement. You can see all the examples in the Official Documention.

Officially, I believe this is called a "labeled break". It's useful for breaking out of nested loops, such as:
found:
for (int i = 0; i < 100; i++)
for (int j = 0; j < 100; i++)
if ( /* Some condition is met */)
break found;
I don't think it's useful for anything else.

I think it's the only case it's used. And it's not something which is commonly used, because it's usually more readable to change the value of a flag to end a loop prematurely.

Create an array (int) of size 10.
Let the user assign the values - (use for-loop).
Find the total and average of the values stored in the array - (use for- loop).