# User:LABoyd2/Conditional and Iterator Functions from manual 151002

### For Loop

Iterate over the values in a vector or range.

Vector version: for (variable=<vector>) <do_something> - <variable> is assigned to each successive value in the vector
Range version: for (variable=<range>) <do_something>

Nested loops : for ( variable1 = <range or vector>, variable2 = <range or vector> ) <do something, using both variables>
for loops can be nested, just as in normal programs. A shorthand is that both iterations can be given in the same for statement

 Usage example 1 - iteration over a vector: ```for (z = [-1, 1]) // two iterations, z = -1, z = 1 { translate([0, 0, z]) cube(size = 1, center = false); } ```
 Usage example 2a - iteration over a range: ```for ( i = [0 : 5] ) { rotate( i * 360 / 6, [1, 0, 0]) translate([0, 10, 0]) sphere(r = 1); } ```
 Usage example 2b - iteration over a range specifying an increment: ```// Note: The middle parameter in the range designation // ('0.2' in this case) is the 'increment-by' value // Warning: Depending on the 'increment-by' value, the // real end value may be smaller than the given one. for ( i = [0 : 0.2 : 5] ) { rotate( i * 360 / 6, [1, 0, 0]) translate([0, 10, 0]) sphere(r = 1); } ```
 Usage example 3 - iteration over a vector of vectors (rotation): ```for(i = [ [ 0, 0, 0], [ 10, 20, 300], [200, 40, 57], [ 20, 88, 57] ]) { rotate(i) cube([100, 20, 20], center = true); } ```
 Usage example 4 - iteration over a vector of vectors (translation): ``` for(i = [ [ 0, 0, 0], [10, 12, 10], [20, 24, 20], [30, 36, 30], [20, 48, 40], [10, 60, 50] ]) { translate(i) cube([50, 15, 10], center = true); } ```

Nested loop example

```  for (xpos=[0:3], ypos = [2,4,6]) // do twelve iterations, using each xpos with each ypos
translate([xpos*ypos, ypos, 0]) cube([0.5, 0.5, 0.5]);
```

### Intersection For Loop

Iterate over the values in a vector or range and take an intersection of the contents.

Note: `intersection_for()` is a work around because of an issue that you cannot get the expected results using a combination of the standard `for()` and `intersection()` statements. The reason is that `for()` does an implicit `union()` of the contents.

Parameters

<loop variable name>
Name of the variable to use within the for loop.
 Usage example 1 - loop over a range: ```intersection_for(n = [1 : 6]) { rotate([0, 0, n * 60]) { translate([5,0,0]) sphere(r=12); } } ```
 Usage example 2 - rotation : ``` intersection_for(i = [ [ 0, 0, 0], [ 10, 20, 300], [200, 40, 57], [ 20, 88, 57] ]) { rotate(i) cube([100, 20, 20], center = true); } ```

### If Statement

Conditionally evaluate a sub-tree.

Parameters

• The boolean expression that should be used as condition

NOTE:

Do not confuse the assignment operator '=' with the equal operator '=='

``` if (a=b) dosomething();  // WRONG - this will FAIL to be processed without any error message
if (a==b) dosomething(); // CORRECT - this will do something if a equals b
```

NOTE:

Assignment is not allowed within either branch of an if statement. Consider using the ternary operator 'condition ? consequent: alternative'.

```// WRONG - this will FAIL to be processed with a syntax error message
if (condition)
{
x = consequent;
} else {
x = alternative;
}
```
```// CORRECT - this will set 'x' to either 'consequent' or 'alternative'
x = condition ? consequent : alternative;
```

Usage example:

```if (x > y)
{
cube(size = 1, center = false);
} else {
cube(size = 2, center = true);
}
```

### Assign Statement

Set variables to a new value for a sub-tree.

Parameters

• The variables that should be (re-)assigned

Usage example:

```for (i = [10:50])
{
assign (angle = i*360/20, distance = i*10, r = i*2)
{
rotate(angle, [1, 0, 0])
translate([0, distance, 0])
sphere(r = r);
}
}
```

Update: [Note: Requires version 2015.03]

Starting with this version, assign() has been deprecated as it is no longer needed; variables can be assigned anywhere.