Loops: How to Repeat Code with for and while

for … to

total = 0.0
for i = 1 to length
    total := total + close[i]

for i = start to end iterates i from start to end inclusive.
When end < start, iteration counts down.
Both bounds are evaluated once at the start of the loop; a change inside the body does not affect iteration count.

Explicit step with `by`

for i = 0 to 100 by 10
    log.info(str.tostring(i))

by is the step magnitude (always positive).
Direction is still inferred from start/end.

for … in

Walks an array:

prices = array.from(100.0, 101.5, 102.0, 103.25)
sum = 0.0
for value in prices
    sum := sum + value

Walk with index as well:

for [index, value] in prices
    log.info(str.tostring(index) + " → " + str.tostring(value))

while

i = 0
remaining = volume
while remaining > 0 and i < 10
    remaining := remaining - 1000
    i := i + 1

Use while when the loop may terminate on a condition that is tested each iteration. Every loop carries a guard of 100,000 iterations per loop per bar: when it trips, that loop exits and the script continues with the next statement (no error is raised). Nested loops are guarded independently.

break and continue

Both work inside any of the three loop forms:

for i = 0 to 100
    if close[i] == 0 or na(close[i])
        continue              // skip this iteration
    if close[i] > close[0] * 2
        break                 // stop the loop entirely
    log.info(str.tostring(close[i]))

Loops as expressions

A loop can produce a value — the result is the value of the last iteration's final statement:

maxGap = for i = 1 to 20
    math.abs(close[i] - close[i - 1])

If the loop never iterates (empty range), the result is na.

Compile-time safety

A loop whose body uses a series-mode function (ta.sma, ta.rsi, …) does not turn that function series-mode-safe — the function still needs to be called on every bar from the top level. The compiler emits a warning.
for … in over na is a no-op.
Modifying the loop array inside a for … in is undefined behaviour; prefer building a new array and swapping references.

Loops