A repeat until block is a type of control block commonly found in visual programming environments and scripting languages. It is designed to execute a sequence of instructions repeatedly until a specific condition you define becomes true.
Based on the provided reference, the core function of a repeat until block can be succinctly stated:
The “repeat until” block in the “Control” category will repeat all of the statements inside of it until a condition that you set is met.
How the Repeat Until Block Functions
Unlike a standard "repeat" block, which runs a set number of times, the repeat until block's execution is governed by a conditional test. The statements within the block are executed repeatedly, and after each execution cycle (or iteration), the specified condition is evaluated. As long as the condition remains false, the loop continues to run. The moment the condition becomes true, the loop stops, and the program proceeds to the next instruction after the block.
Think of it like telling someone to "keep stirring the soup until it thickens." You don't tell them how many times to stir; you tell them to stop when the desired state (thickened) is reached.
Practical Applications
Repeat until blocks are useful when you don't know in advance how many times a task needs to be performed, but you know the end state that should stop the task.
Here are a few common scenarios where you might use a repeat until block:
- Waiting for User Input: Repeat prompting the user for input until they enter a valid value (e.g., a number within a certain range).
- Animation or Movement: Keep moving an object until it reaches a specific position or collides with another object.
- Simulation: Run a simulation step by step until a certain event occurs or a target value is reached.
- Gameplay: Continue a game loop until the player's score reaches a certain point or their health drops to zero.
Repeat vs. Repeat Until
While both are control blocks used for repetition, they differ in how the loop terminates. The reference briefly contrasts the two:
| Block Type | Termination Condition |
|---|---|
| Repeat | Runs a set, predefined number of times. |
| Repeat Until | Runs until a specific condition that you set is met. |
In essence, a repeat block is count-controlled, while a repeat until block is condition-controlled.
Understanding the repeat until block is fundamental for creating dynamic and responsive programs where actions need to continue based on changing conditions rather than a fixed count.
