> ## Documentation Index > Fetch the complete documentation index at: https://docs.ntop.com/llms.txt > Use this file to discover all available pages before exploring further. # If-Else *** ## About this Block ### What it does: The **If-Else** block provides control flow to your nTop workflow, enabling it to make decisions based on a condition. It evaluates the boolean *Condition* input and returns the *Then* branch if the *Condition* is true or the Else branch if the *Condition* is false. We will refer to both *Then* and *Else* outputs as "branches." Below is a common schematic of the If-Else. ![If Else Flow Chart](https://storage.googleapis.com/files-learn/static/ExtendedBlockDocs/if_else_flow_chart.png) ### Running: To better understand **If-Else**, it is important to understand how the nTop notebook blocks are ran. When you place blocks into the notebook, the block will always run unless: * The block’s required inputs are empty * The block is set to Manual Run Mode * Any block referenced by the block upstream does not have its required inputs entered * Any block referenced by the block upstream is set to Manual Run Mode * Autorun is toggled off **If-Else** works differently than other nTop blocks - when set up correctly, only the *Then* or *Else* branch will run based on the Condition, returning that output value to the **If-Else** block. Your nTop workflow not running the unneeded branch is beneficial if you run computationally expensive workflows (e.g., meshing) or have a branch that produces a failure. **Common uses:** * General Logic * Mesh Setup * Simulation Setup * Scan Data Alignment * Field Logic **Tips:** * When **If-Else** branches are made into variables, they will always run. When running computationally expensive branches of **If-Else**, we recommend not making the branches variables. ![If Else Example](https://storage.googleapis.com/files-learn/static/ExtendedBlockDocs/if_else_running.gif) * We recommend only referencing the **If-Else** output properties downstream, not the output properties from either of the branches. If you do reference the output properties of a branch downstream, nTop will require this branch to run regardless of the *Condition*. * If needed, create branch nestings and make variables of lower-level nestings. * The bracket example below shows the correct setup. * The "Implicit->Mesh," "Amount," and "Edge length" variables are used in both branches of **If-Else** so that they can be kept as variables outside of **If-Else**. * (Red Arrow) The "Simple" mesh is self-intersecting. In this instance, the output property of the "self-intersecting" boolean equals True and is used as the *Condition*. * Due to the *Condition* being True, only the "Then - Volume Mesh" branch runs, providing a suitable mesh. * Due to the *Condition* being True, the "Else - Volume Mesh" branch does not run and returns an error. ![If Else Example Self-intersection](https://storage.googleapis.com/files-learn/static/ExtendedBlockDocs/if_else_example_self_intersection.png) * When creating notebooks, you will likely create the blocks you need in the notebook and then drag them into the branches of the **If-Else**. * These blocks will run automatically until they are used as Branches in **If-Else** - in which case only the one that matches the *Condition* input will run. This is very helpful for reusable workflows. * If you want to ensure neither branch is ever run, ensure the *Condition* is unbuilt or in Manual Run Mode, then create your logic encapsulated in the If-Else via the input dropdown. * The two overloads of **If-Else** enable you to leverage a Bool Field *Condition* to return either a Scalar Field or Vector Field value. Since evaluating fields leverages mathematics, both branches will always run for these overloads and be computationally fast. ![If Else Example Bool Field Overloads](https://storage.googleapis.com/files-learn/static/ExtendedBlockDocs/if_else_example_bool_field_overloads.gif) ***

Bool, Any, Any

Returns a value based on a given condition. ### Inputs | Name | Type | Description | | --------- | -------------------------------------------------- | ------------------------------------- | | Condition | [Bool](../../../../block-documentation/types/bool) | Condition used to evaluate execution. | | Then | [Any](../../../../block-documentation/types/any) | Output when the Condition is True. | | Else | [Any](../../../../block-documentation/types/any) | Output when the Condition is False. | ### Outputs | Type | | ------------------------------------------------ | | [Any](../../../../block-documentation/types/any) | ***

Bool Field, Scalar Field, Scalar Field

Returns a field of values evaluated based on a given condition. ### Inputs | Name | Type | Description | | --------- | ------------------------------------------------------------------ | ------------------------------------------------------------------------- | | Condition | [Bool Field](../../../../block-documentation/types/bool-field) | Condition used to evaluate execution at a field point. | | Then | [Scalar Field](../../../../block-documentation/types/scalar-field) | Output when the field value of Condition is True at the evaluated point. | | Else | [Scalar Field](../../../../block-documentation/types/scalar-field) | Output when the field value of Condition is False at the evaluated point. | ### Outputs | Type | | ------------------------------------------------------------------ | | [Scalar Field](../../../../block-documentation/types/scalar-field) | ***

Bool Field, Vector Field, Vector Field

Returns a field of values evaluated based on a given condition. ### Inputs | Name | Type | Description | | --------- | ------------------------------------------------------------------ | ------------------------------------------------------------------------- | | Condition | [Bool Field](../../../../block-documentation/types/bool-field) | Condition used to evaluate execution at a field point. | | Then | [Vector Field](../../../../block-documentation/types/vector-field) | Output when the field value of Condition is True at the evaluated point. | | Else | [Vector Field](../../../../block-documentation/types/vector-field) | Output when the field value of Condition is False at the evaluated point. | ### Outputs | Type | | ------------------------------------------------------------------ | | [Vector Field](../../../../block-documentation/types/vector-field) | ***

Bool Field, 2D Vector Field, 2D Vector Field, 5.31.0

Returns a field of values evaluated based on a given condition. ### Inputs | Name | Type | Description | | --------- | ------------------------------------------------------------------------ | ------------------------------------------------------------------------- | | Condition | [Bool Field](../../../../block-documentation/types/bool-field) | Condition used to evaluate execution at a field point. | | Then | [2D Vector Field](../../../../block-documentation/types/2d-vector-field) | Output when the field value of Condition is True at the evaluated point. | | Else | [2D Vector Field](../../../../block-documentation/types/2d-vector-field) | Output when the field value of Condition is False at the evaluated point. | ### Outputs | Type | | ------------------------------------------------------------------------ | | [2D Vector Field](../../../../block-documentation/types/2d-vector-field) |