# For loop ## Simple loop ### Syntax `for , ` * `init` is an **initializer**, explained [below](/the-language/control-flow/for-loop.md#the-initializer) * `end` is an expression, the value which initial variable iterates through to * `body` is a statement ### The initializer It could be: #### A variable declaration ```javascript for var i = 0 ... for let j = 0 ... ``` Use #### A assign expression ```javascript var i = 0 for i ... ``` If the target vairable in the assignment is not defined, it will be defined by the **let** keyword implicitly. ```javascript for j = 0 ... // like: for let j = 0 ... ``` ### Examples #### Counting numbers ```lua for i = 1, 10 { puts i } ``` #### Printing even numbers ```lua for i = 0, 20 { if i % 2 == 0 { puts i } } ``` #### Counting down ```lua for i = 20, 1 { puts i } ``` ## C-style loop But no parenthese, comma instead of semicolon. ### Syntax `for , , ` * `init` is loop initializer, it could be an expression * `cond` is loop condition, an expression * `updater` is an expression, which is executed after the loop body ### Examples #### Basic ```c for i = 0, i < 5, i++ { // do something } ``` #### Without updater ```javascript for i = 0, i < 5, { i++ // own updater } ``` {% hint style="warning" %} If the last comma is removed, the loop becomes [**Simple loop**](/the-language/control-flow/for-loop.md#simple-loop). {% endhint %} ## For-each loop Iterating through an array, map. ### Syntax `for [, ] : ` * `first` - the first variable * `second` - the second variable (optional) * `expr` - an expression to be evaluated, value must be a map or an array ### Examples With an array: ```javascript var arr = [1, 2, 3] for v, i : arr { puts v, i // value - index } ``` Just use `for v : arr` to get the value only. ```javascript for v : arr { puts v } ``` With a map: ```javascript var map = { a: 4, b: 5, c: 6 } for k, v : map { puts k, v // key - value } ``` Depend on the implementation, the key - value pairs may not in input order. So the output of above example could be: ``` a 4 b 5 c 6 ``` ... or ``` b 5 c 6 a 4 ``` Like array, just get the key only: ```javascript for k : map { puts k } ``` ## Infinite loop #### Pure ```javascript for { // Do something } ``` #### With initializer ```javascript for i = 1 { puts i++ } ``` --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://aup.nomi.dev/the-language/control-flow/for-loop.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.