# Nested and Sequential IF Conditionals

**Nested IF** conditionals allow Bitcoin Script to implement complex **multi-condition logic** similar to switch/case statements. By placing IF statements inside other IF blocks, you create decision trees with multiple possible execution paths.

#### Nested structure:

```
<Case 1 check>
OP_IF
  <When 1 action>
OP_ELSE
  <Case 2 check>
  OP_IF
    <When 2 action>
  OP_ELSE
    <Default action>
  OP_ENDIF
OP_ENDIF
```

#### How nested IF conditionals work:

The first condition is evaluated. If TRUE, execute first action block and skip all nested conditionals. If FALSE, enter the ELSE block and evaluate the second condition. This continues for additional conditions, with the final ELSE catching all remaining cases.

#### Practical example:

```
<locktime> [Use OP_PUSH_TX to extract nLockTime] OP_DROP OP_1
OP_IF
  <timeout_pubkey> OP_CHECKSIG // Path 1: After timeout
OP_ELSE
  <is_emergency> 
  OP_IF
    OP_2 <pk1> <pk2> <pk3> OP_3 OP_CHECKMULTISIG // Path 2: Emergency
  OP_ELSE
    <primary_pubkey> OP_CHECKSIG // Path 3: Normal
  OP_ENDIF
OP_ENDIF
```

This implements three spending paths: after timelock (simple signature), emergency before timeout (2-of-3 multisig), or normal spending (primary key).

#### Alternative: Sequential IF conditionals

Instead of nesting, you can write separate IF statements sequentially:

```
<Case 1 check>
OP_IF
  <When 1 action>
OP_ENDIF

<Case 2 check>
OP_IF
  <When 2 action>
OP_ENDIF
```

&#x20;

#### Comparative Approaches

| **Aspect**             | **Nested IF conditionals** | **Sequential IF conditionals** |
| ---------------------- | -------------------------- | ------------------------------ |
| **Evaluation**         | Stops at first match       | Evaluates all conditions       |
| **ENDIF tracking**     | Complex with depth         | Simple (one per IF)            |
| **Mutual exclusivity** | Automatic via ELSE         | Must ensure manually           |
| **Readability**        | Harder with deep nesting   | Clearer at each level          |

#### When to use each:

* Use **nested IF** conditionals when conditions are mutually exclusive and form a decision tree
* Use **sequential IF** conditionals when conditions are independent or structure clarity is priority


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