====== Loops ======

You always need a loop structure if you want to repeat anything.

For loops we use the keyword "do". do allows you to use two additional variables: //value// and //index//. //value// is the current value, index increases from zero by 1 for every step. If you don't use these variables, they will not cost any time.

Do works in several operating modes

==== Condition ====

This represents the common while-loop in programming languages like C. If you put an condition in front of the keyword //do// the loop will be repeated until the conditions becomes false.

<code>
i is 10

i > 0 do
  print i$, "\n";
</code>

For an infinite loop use
<code>
true do
  printf "infinite\n";
</code>

You can use the variable //index// to ask in which iteration you are:

<code>
true do
  printf index$, " iteration of infinite loop\n";
</code>
which will result into
<code>
0 iteration of infinite loop
1 iteration of infinite loop
2 iteration of infinite loop
...
</code>

==== Counting ====

The easiest way of repeating things is to count how often you want to do the given content. You simply use an unsigned integer in front of the //do// keyword. You can use //index// for the count of fulfilled iterations (starting at 0) or value for the current iteration (starting at 1).

<code>
5 do
  print "Index: ", index$, " Value: ", value$, "\n";
</code>

The result is
<code>
Index: 0 Value 1
Index: 1 Value 2
Index: 2 Value 3
Index: 3 Value 4
Index: 4 Value 5
</code>

Of course you can use a variable of type //unsigned int//:

<code>
i is 5;

i do
  print "Index: ", index$, " Value: ", value$, "\n";
</code>

===== Iterating through ranges =====

You can also use ranges to iterate. 
<code>
12..15 do
  print "Index: ", index$, " Value: ", value$, "\n";
</code>
results into:
<code>
Index: 0 Value 12
Index: 1 Value 13
Index: 2 Value 14
</code>

Pay attention that the beginning element of the range is included, the end element of the range is excluded. So if you want to iterate from 'a' to 'z' just add 1, so 'z' is included.

<code>
'a'..'z'+1 do
  print "Index: ", index$, " Value: ", value$, "\n";
</code>
results into:
<code>
Index: 0 Value a
Index: 1 Value b
Index: 2 Value c
...
Index: 23 Value x
Index: 24 Value y
Index: 25 Value z
</code>

===== Iterating through collections =====

Collections are everything which contains multiple elements like arrays, strings, lists.

The easiest way to do an iteration is to take an collection data type (i.e. a List or an Array) and iterate.

<code>
char word[] = "Genesys";

print "The word is: ",

for( char c in word )
  print c$;
  
print "\n";
</code>

You can use an integer array to count.
<code>
{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 } do
  print value$;
</code>
which will result in
<code>  
1
2
..
9
10
</code>

===== for =====

You have already seen the for-each version before. With Genesys you can also use a more c style for-loops:

<code>
for( int i:10; i > 0; i-- )
  print "i: ", i, "\n";
</code>

==== do.. while ====

This type of loops is used if the instructions need to be proceeded at least once. At the end of the instruction block you see the while expression deciding if the loop will be proceeded again.

<code>
int i=10;

do
  print "i: ", i--, "\n";
while( i > 0 )
</code>

You see, that this loop will result in slightly different results. To get the same result you have to use --i instead of i--.

===== Breaking from a Loop or Continuation =====

As in C you can break a loop with the keyword ''break''. The following loop will count from 1 to 4 and will be broken before 5 is printed.

<code>
1..10 do
{
  index == 5 then break;
  
  print index$, "\n";
}
</code>

With ''continue'' you jump at the top of a loop, ignoring everything following:

Here the loop count from 1 to 10 but the number 5 is missing:

<code>
1..10 do
{
  index == 5 then continue;
  
  print index$, "\n";
}
</code>

===== Named Loops =====

If you nest a loop within another you will get trouble with ''index'' and ''value''. They are always defined for the loop you're inside.
If you want to touch a 3x3 matrix you can use two loops:

<code>
{ 1..3 } :=
  { 1..3 } :=
    print value$, "/", value$, "\n";
</code>

That won't work of course.
To get the right index you have to name at least the outer loops:
<code>
x is { 1..3 } :=
  y is { 1..3 } :=
    print x.value$, "/", y.value$, "\n";
</code>

You do not need to give ''y'' its name. ''value'' will reference to the inner loop which is the y-loop.

This also works for 'for' and while loops. 
Please note that ''inner.index'' is not equal to ''i'' and ''outer.index'' is not equal to ''o''.

<code>
outer is for( int o : -2; o < 10; o++ )
{
  inner is for( int i : -2; i < 10; i++ )
  {
    if( o == 1 && i == 2 ) break;           // jumps after inner loop
    if( o == 2 && i == 4 ) break inner;     // jumps after inner loop
    
    if( o == 3 && i == 4 ) continue;        // jumps to inner loop at i++
    if( o == 3 && i == 6 ) continue inner;  // jumps to inner loop at i++

    if( o == 4 && i == 8 ) continue outer;  // jumps to outer loop at o++
    if( o == 5 && i == 8 ) break outer;     // jumps after outer loop
    
    print "outer: ", outer.index$, "/", o, "; ";
    print "inner: ", inner.index$, "/", i, "\n";
  }
  // after inner loop
}
// after outer loop
</code>

You can proceed like this with while
<code>
outer is while( true )
  inner is while( true )
    break inner;
</code>

or do.. while()
<code>
outer is do
  inner is do
    break outer;
  while( true )
while( true )
</code>