Source: https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/control-flow/
Documentation version: v5.3.2

# Control flow statements

The control flow statements control the execution order of statements in a [procedure](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/procedures/create/).

The following control flow statements are supported:

- `WHILE`: executes a series of statements in a loop for as long as a specified condition is true.
- `IF`: executes a series of statements based on a specified condition.
- `BREAK`: exits a loop immediately. It is typically used within a WHILE statement or within an IF statement that is inside a loop.
- `CONTINUE`: skips the remaining statements in the current iteration and proceeds to the next iteration. It is typically used within a WHILE statement or within an IF statement that is inside a loop.

## Syntax

diagramsource

 while_statement if_statement break_statement continue_statement  

````
while_statement ::=
  'WHILE' value_expression 'THEN' '{' procedure_body '}'

if_statement ::=
  'IF' value_expression 'THEN' '{'  procedure_body '}' 
  ( 'ELSEIF' value_expression 'THEN' '{'  procedure_body  '}' )*
  ( 'ELSE' '{'  procedure_body  '}' )?   

break_statement ::=
  'BREAK'    

continue_statement ::=
  'CONTINUE'     

````

## Parameters

### `value_expression`

A value expression that evaluates to a boolean value. For more information, see [Boolean type](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/data-types/boolean-type/) and [Expressions](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/fe/#value_expressions).

### `procedure_body`

A set of statements to be executed. For more information, see [Procedure body](https://dev-docs.nebula-graph.io/v5.3.2/database-gql-reference/procedures/create/#procedure_body).

## Examples

### WHILE

````
'''
VALUE i INT = 0 
WHILE i < 5 THEN { 
  SET i = i + 1 
} 
RETURN i
'''

````

Return:

````
+---+
| i |
+---+
| 5 |
+---+

````

### IF

#### IF-ELSE

````
'''
VALUE i INT = 5 
IF i < 5 THEN { 
  SET i = i + 1 
} ELSE { 
  SET i = i - 1 
} 
RETURN i
'''

````

Return:

````
+---+
| i |
+---+
| 4 |
+---+

````

#### IF-ELSEIF-ELSE

````
'''
VALUE i INT = 4 
IF i < 3 THEN { 
  SET i = i + 1 
} ELSEIF i < 5 THEN { 
  SET i = i + 2 
} ELSE { 
  SET i = i - 1 
} 
RETURN i
'''

````

Return:

````
+---+
| i |
+---+
| 6 |
+---+

````

### BREAK

````
'''
VALUE i INT = 0 
WHILE i < 5 THEN { 
  IF i = 3 THEN { 
    BREAK 
    } 
  SET i = i + 1 
} 
RETURN i 
'''

````

Return:

````
+---+
| i |
+---+
| 3 |
+---+

````

### CONTINUE

````
'''
VALUE i INT = 0 
WHILE i < 5 THEN { 
  IF i < 3 THEN { 
    SET i = i + 1 
    CONTINUE 
  } ELSE { 
    SET i = i + 1 
  } 
} 
RETURN i
'''

````

Return:

````
+---+
| i |
+---+
| 5 |
+---+

````