This documentation explains various loop constructs for repeating actions, conditional execution, iterating over ranges and arrays, and terminating loops.
Repeating Actions in Several Times
Repeat 4 times
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><block type=\"controls_repeat_ext\"><value name=\"TIMES\"><shadow type=\"math_whole_number\"><field name=\"NUM\">4</field></shadow></value></block></xml>"}
This is used to do some actions in several times.
Parameters: Condition: Number (Default: 4)
Output: N/A
Sample code:
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><variables><variable>mainLayout</variable><variable>mainScreen</variable></variables><block type=\"pxt-on-start\" x=\"0\" y=\"0\"><statement name=\"HANDLER\"><block type=\"variables_set\"><field name=\"VAR\">mainLayout</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"ScreenItem_createLayout\"/></value><next><block type=\"variables_set\"><field name=\"VAR\">mainScreen</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"Screen_create\"><value name=\"label\"><shadow type=\"text\"><field name=\"TEXT\">Main</field></shadow></value><value name=\"layout\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value></block></value><next><block type=\"controls_repeat_ext\"><value name=\"TIMES\"><shadow type=\"math_whole_number\"><field name=\"NUM\">4</field></shadow></value><statement name=\"DO\"><block type=\"ScreenItem_Layout_add\"><value name=\"this\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value><value name=\"item\"><block type=\"Control_createTextBlock\"><mutation xmlns=\"http://www.w3.org/1999/xhtml\" _expanded=\"1\" _input_init=\"true\"></mutation><value name=\"text\"><shadow type=\"text\"><field name=\"TEXT\">Hello</field></shadow></value></block></value></block></statement></block></next></block></next></block></statement></block></xml>"}
The output:
Doing Actions when Meeting the Boolean Conditions
While false do
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><block type=\"device_while\"><value name=\"COND\"><shadow type=\"logic_boolean\"><field name=\"BOOL\">FALSE</field></shadow></value></block></xml>"}
This block is used to run the same actions when it is meeting the condition.
Parameters: Display setting: Boolean (True/False [Default])
Output: N/A
Sample code:
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><variables><variable>mainLayout</variable><variable>mainScreen</variable></variables><block type=\"pxt-on-start\" x=\"0\" y=\"0\"><statement name=\"HANDLER\"><block type=\"variables_set\"><field name=\"VAR\">mainLayout</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"ScreenItem_createLayout\"/></value><next><block type=\"variables_set\"><field name=\"VAR\">mainScreen</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"Screen_create\"><value name=\"label\"><shadow type=\"text\"><field name=\"TEXT\">Main</field></shadow></value><value name=\"layout\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value></block></value><next><block type=\"device_while\"><value name=\"COND\"><shadow type=\"logic_boolean\"><field name=\"BOOL\">FALSE</field></shadow></value><statement name=\"DO\"><block type=\"ScreenItem_Layout_add\"><value name=\"this\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value><value name=\"item\"><block type=\"Control_createTextBlock\"><mutation xmlns=\"http://www.w3.org/1999/xhtml\" _expanded=\"1\" _input_init=\"true\"></mutation><value name=\"text\"><shadow type=\"text\"><field name=\"TEXT\">Showing text after 5 seconds.</field></shadow></value></block></value><next><block type=\"Task_sleep\"><value name=\"ms\"><shadow type=\"math_number\"><field name=\"NUM\">5000</field></shadow></value></block></next></block></statement></block></next></block></next></block></statement></block></xml>"}
While false, the output:
While true, the output:
Doing Actions when Taking Values from Zero to Final
For index from 0 to 4
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><block type=\"controls_repeat_ext\"><value name=\"TIMES\"><shadow type=\"math_whole_number\"><field name=\"NUM\">4</field></shadow></value></block></xml>"}
This block is used to do action when taking the values from 0 to the final number which will count by 1.
Parameters:
- Index
- Condition: Number (Default: 4)
Output: N/A
Sample code:
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><variables><variable>mainLayout</variable><variable>mainScreen</variable><variable>index</variable></variables><block type=\"pxt-on-start\" x=\"0\" y=\"0\"><statement name=\"HANDLER\"><block type=\"variables_set\"><field name=\"VAR\">mainLayout</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"ScreenItem_createLayout\"/></value><next><block type=\"variables_set\"><field name=\"VAR\">mainScreen</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"Screen_create\"><value name=\"label\"><shadow type=\"text\"><field name=\"TEXT\">Main</field></shadow></value><value name=\"layout\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value></block></value><next><block type=\"pxt_controls_for\"><value name=\"VAR\"><shadow type=\"variables_get_reporter\"><field name=\"VAR\">index</field></shadow></value><value name=\"TO\"><shadow type=\"math_whole_number\"><field name=\"NUM\">4</field></shadow></value><statement name=\"DO\"><block type=\"ScreenItem_Layout_add\"><value name=\"this\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value><value name=\"item\"><block type=\"Control_createTextBlock\"><mutation xmlns=\"http://www.w3.org/1999/xhtml\" _expanded=\"1\" _input_init=\"true\"></mutation><value name=\"text\"><shadow type=\"text\"><field name=\"TEXT\">It will repeat 5 times.</field></shadow></value></block></value></block></statement></block></next></block></next></block></statement></block></xml>"}
The output:
Doing Actions when Taking Value in the Length of Array
For element value of list
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><block type=\"pxt_controls_for_of\"><value name=\"VAR\"><shadow type=\"variables_get_reporter\"><field name=\"VAR\">value</field></shadow></value><value name=\"LIST\"><shadow type=\"variables_get\"><field name=\"VAR\">list</field></shadow></value></block></xml>"}
This block is used to do some actions when taking value in the array one by one until the end of list.
Parameters:
- Value
- Array
Output: N/A
Sample code:
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><variables><variable>mainLayout</variable><variable>mainScreen</variable><variable>list</variable><variable>value</variable></variables><block type=\"pxt-on-start\" x=\"0\" y=\"0\"><statement name=\"HANDLER\"><block type=\"variables_set\"><field name=\"VAR\">mainLayout</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"ScreenItem_createLayout\"/></value><next><block type=\"variables_set\"><field name=\"VAR\">mainScreen</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"Screen_create\"><value name=\"label\"><shadow type=\"text\"><field name=\"TEXT\">Main</field></shadow></value><value name=\"layout\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value></block></value><next><block type=\"variables_set\"><field name=\"VAR\">list</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"lists_create_with\"><mutation items=\"3\" horizontalafter=\"3\"/><value name=\"ADD0\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow></value><value name=\"ADD1\"><shadow type=\"math_number\"><field name=\"NUM\">1</field></shadow></value><value name=\"ADD2\"><shadow type=\"math_number\"><field name=\"NUM\">2</field></shadow></value></block></value><next><block type=\"pxt_controls_for_of\"><value name=\"VAR\"><shadow type=\"variables_get_reporter\"><field name=\"VAR\">value</field></shadow></value><value name=\"LIST\"><block type=\"variables_get\"><field name=\"VAR\">list</field></block></value><statement name=\"DO\"><block type=\"ScreenItem_Layout_add\"><value name=\"this\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value><value name=\"item\"><block type=\"Control_createTextBlock\"><mutation xmlns=\"http://www.w3.org/1999/xhtml\" _expanded=\"1\" _input_init=\"true\"></mutation><value name=\"text\"><shadow type=\"text\"><field name=\"TEXT\">It will repeat 3 times.</field></shadow></value></block></value></block></statement></block></next></block></next></block></next></block></statement></block></xml>"}
The output:
Terminate the Current Loop
Break
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><block type=\"break_keyword\"/></xml>"}
This block is used to stop the current loop.
Parameters: N/A
Output: N/A
Sample code:
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><variables><variable>mainLayout</variable><variable>mainScreen</variable></variables><block type=\"pxt-on-start\" x=\"0\" y=\"0\"><statement name=\"HANDLER\"><block type=\"variables_set\"><field name=\"VAR\">mainLayout</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"ScreenItem_createLayout\"/></value><next><block type=\"variables_set\"><field name=\"VAR\">mainScreen</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"Screen_create\"><value name=\"label\"><shadow type=\"text\"><field name=\"TEXT\">Main</field></shadow></value><value name=\"layout\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value></block></value><next><block type=\"device_while\"><value name=\"COND\"><shadow type=\"logic_boolean\"><field name=\"BOOL\">TRUE</field></shadow></value><statement name=\"DO\"><block type=\"ScreenItem_Layout_add\"><value name=\"this\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value><value name=\"item\"><block type=\"Control_createTextBlock\"><mutation xmlns=\"http://www.w3.org/1999/xhtml\" _expanded=\"1\" _input_init=\"true\"></mutation><value name=\"text\"><shadow type=\"text\"><field name=\"TEXT\">It will show once only.</field></shadow></value></block></value><next><block type=\"break_keyword\"/></next></block></statement></block></next></block></next></block></statement></block></xml>"}
The output:
Doing Next Action
Continue
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><block type=\"continue_keyword\"/></xml>"}
This is used to skip the current action and continue with the next action in the loop.
Parameters: N/A
Output: N/A
Sample code:
{"blocks":"<xml xmlns=\"https://developers.google.com/blockly/xml\"><variables><variable>mainLayout</variable><variable>mainScreen</variable><variable>index</variable></variables><block type=\"pxt-on-start\" x=\"0\" y=\"0\"><statement name=\"HANDLER\"><block type=\"variables_set\"><field name=\"VAR\">mainLayout</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"ScreenItem_createLayout\"/></value><next><block type=\"variables_set\"><field name=\"VAR\">mainScreen</field><value name=\"VALUE\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"Screen_create\"><value name=\"label\"><shadow type=\"text\"><field name=\"TEXT\">Main</field></shadow></value><value name=\"layout\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value></block></value><next><block type=\"pxt_controls_for\"><value name=\"VAR\"><shadow type=\"variables_get_reporter\"><field name=\"VAR\">index</field></shadow></value><value name=\"TO\"><shadow type=\"math_whole_number\"><field name=\"NUM\">4</field></shadow></value><statement name=\"DO\"><block type=\"controls_if\"><value name=\"IF0\"><shadow type=\"logic_boolean\"><field name=\"BOOL\">TRUE</field></shadow><block type=\"logic_compare\"><field name=\"OP\">EQ</field><value name=\"A\"><shadow type=\"math_number\"><field name=\"NUM\">0</field></shadow><block type=\"variables_get\"><field name=\"VAR\">index</field></block></value><value name=\"B\"><shadow type=\"math_number\"><field name=\"NUM\">3</field></shadow></value></block></value><statement name=\"DO0\"><block type=\"continue_keyword\"/></statement><next><block type=\"ScreenItem_Layout_add\"><value name=\"this\"><block type=\"variables_get\"><field name=\"VAR\">mainLayout</field></block></value><value name=\"item\"><block type=\"Control_createTextBlock\"><mutation xmlns=\"http://www.w3.org/1999/xhtml\" _expanded=\"1\" _input_init=\"true\"></mutation><value name=\"text\"><block type=\"text_join\"><mutation items=\"2\"/><value name=\"ADD0\"><shadow type=\"text\"><field name=\"TEXT\">The number is </field></shadow></value><value name=\"ADD1\"><shadow type=\"text\"><field name=\"TEXT\"/></shadow><block type=\"variables_get\"><field name=\"VAR\">index</field></block></value></block></value></block></value></block></next></block></statement></block></next></block></next></block></statement></block></xml>"}
The output:
Table of Content