ReactCHALLENGES

1. While

A while loop repeats a block of code as long as a condition stays True:

  • condition — any expression that produces True or False; it is checked before each pass.
  • The block runs only while the condition is True. When it becomes False, the loop stops and the program continues after it.
  • The block must change something the condition depends on. If nothing changes, the condition stays True and the loop never ends. That is an infinite loop.

The first pass prints 3; then countdown becomes 2, the condition is checked again, and so on until countdown is 0 and 0 > 0 is False.

A variable that is initialized before the loop and updated inside it to control the condition is called a counter.

#01

Count down with a while loop

Start n at 3. While n is greater than 0, print n and then subtract 1 from it with n -= 1.

Print exactly:

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#02

Repeat while a condition holds

Start n at 1. While n is less than 20, print n and then double it with n *= 2. The last printed value is 16, because 32 is not less than 20.

Print exactly:

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#03

Stop when a balance reaches zero

Start balance at 150. While balance is greater than 0, print it and subtract 50 with balance -= 50.

Print exactly:

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