## Keyboard shortcuts

Press `←` or `→` to navigate between chapters

Press `S` or `/` to search in the book

Press `?` to show this help

Press `Esc` to hide this help

- Auto
- Light
- Dark

# Algorand Specifications

Constants can be pushed onto the Stack in two different ways:

1. Constants can be pushed directly with `pushint` or `pushbytes` opcodes. This method is more efficient for constants that are only used once.

2. Constants can be loaded into storage separate from the Stack and Scratch Space, with `intcblock` or `bytecblock` opcodes. Then, constants from this storage can be pushed onto the Stack by referring to the type and index using `intc`, `intc_[0123]`, `bytec`, and `bytec_[0123]`. This method is more efficient for constants that are used multiple times.

The opcodes `intcblock` and `bytecblock` use [proto-buf style variable length unsigned int](https://developers.google.com/protocol-buffers/docs/encoding#varint), reproduced [in the `varuint` section](https://specs.algorand.co/avm/avm-versioning#encoding).

The `intcblock` opcode is followed by a `varuint` specifying the number of integer constants, and then that number of `varuint`.

The `bytecblock` opcode is followed by a `varuint` specifying the number of byte constants, and then that number of pairs of `(varuint, bytes)` length prefixed byte strings.

The [Assembler](https://specs.algorand.co/avm/avm-assembler) will hide most of this, for example, allowing simple use of `int 1234` and `byte 0xcafed00d`. Constants introduced via `int` and `byte` will be assembled into appropriate uses of `pushint|pushbytes` and `{int|byte}c, {int|byte}c_[0123]` to minimize program bytecode size.

An _application call_ transaction **MUST** indicate the action to be taken following the execution of its Approval Program or Clear State Program.

The constants below describe the available actions.

| ACTION | VALUE | DESCRIPTION |
| --- | --- | --- |
| `NoOp` | `0` | _Only_ execute the Approval Program associated with the _application ID_, with no additional effects. |
| `OptIn` | `1` | _Before_ executing the Approval Program, allocate _local state_ for this _application ID_ into the _sender_’s account data. |
| `CloseOut` | `2` | _After_ executing the Approval Program, clear any _local state_ for this _application ID_ out of the _sender_’s account data. |
| `ClearState` | `3` | _Do not_ execute the Approval Program, and instead execute the Clear State Program (which may not reject this transaction). Additionally, clear any _local state_ for the _application ID_ out of the _sender_’s account data (as in `CloseOutOC`). |
| `UpdateApplication` | `4` | _After_ executing the Approval Program, _replace_ the Approval Program and Clear State Program associated with the _application ID_ with the programs specified in this transaction. |
| `DeleteApplication` | `5` | _After_ executing the Approval Program, _delete_ the parameters of with the _application ID_ from the account data of the application’s creator. |

| TYPE | VALUE | DESCRIPTION |
| --- | --- | --- |
| `unknown` | `0` | Unknown type, invalid transaction |
| `pay` | `1` | ALGO transfers (payment) |
| `keyreg` | `2` | Consensus keys registration |
| `acfg` | `3` | Asset creation and configuration |
| `axfer` | `4` | Asset transfer |
| `afrz` | `5` | Asset freeze and unfreeze |
| `appl` | `6` | Application calls |
| `stpf` | `7` | State Proof |
| `hb` | `8` | Consensus heartbeat |