# 4. Control Flow

## if / elif / else
```stencil
let n = 7;
if (n > 10) {
    print("big");
} elif (n > 5) {
    print("medium");
} else {
    print("small");
}
```
Parentheses around the condition are optional:
```stencil
if n > 5 {
    print("more than five");
}
```

## while
```stencil
let i = 0;
while (i < 3) {
    print("i =", i);
    i = i + 1;
}
```

## for — C-style
```stencil
for (let i = 0; i < 5; i = i + 1) {
    print(i);   // 0 1 2 3 4
}
```

## for ... in — foreach
Iterate a list, a string (its characters), or a dict (its keys):
```stencil
for x in [10, 20, 30] {
    print(x);
}
for ch in "abc" {
    print(ch);
}
for key in { "a": 1, "b": 2 } {
    print(key);
}
```

## loop ... in — ranges
`a..b` goes from `a` up to (but not including) `b`:
```stencil
loop i in 0..5 {
    print(i);   // 0 1 2 3 4
}
```
`loop { ... }` with no range is an infinite loop.

## Ternary expression
```stencil
let x = 8;
let label = x % 2 == 0 ? "even" : "odd";
print(label);   // even
```

## A note on break/continue
There is no `break`/`continue` keyword yet. Use a boolean flag, or wrap the loop in a function and `return`:
```stencil
func firstEven(list) {
    for x in list {
        if (x % 2 == 0) { return x; }   // returns out of the loop
    }
    return null;
}
print(firstEven([1, 3, 6, 9]));   // 6
```

Next: [Functions](05_functions.md)