学ぶ while loop (2/2)

セクション 6. 章 2

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As we mentioned before, sometimes we don't exactly know the stopping condition. In that case, we first need to start an infinite loop and then specify the stopping condition. If you want to start an infinite loop, use while True.

There are two important commands in Python: break and continue. break will break the loop and go outside loop to the next line. continue will skip all the rest code inside loop and return at its beginning.

For example, imagine we have number 3 and want to reach number 6. All we can do - is to add 2 and subtract 1.


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# starting number
a = 3

# let's construct while loop
while True: # infinite loop
  if a == 6: # stopping condition
    print("Number", a, "reached")
    break # this will break loop
  elif a < 6: # if less, than add 2
    a = a + 2
    print("Adding 2... Reached", a)
    continue # returning to loop start
  else: # if greater, then subtract 1
    a = a - 1
    print("Subtracting 1... Reached", a)
    continue # returning to loop start

If we didn't specify break in the first if, then we got an infinite loop, because 6 is not satisfying any other condition but the first one. In that case, it printed us "Number 6 reached" infinite times.

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Using while loop and continue/break commands construct the next program:

Given number a = -7. At each step if the number is negative, you need to print "a is negative, and =" and value, and then add 4 and continue the loop. If the number is positive, you need to print "a is positive, and =" and its value after = sign. In that case you need to subtract 3 and continue the loop. If the number is zero - you need to print "Finally a is zero!" and break the loop.

解答

実践的な練習のためにデスクトップに切り替える下記のオプションのいずれかを利用して、現在の場所から続行する

すべて明確でしたか？

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セクション 6. 章 2

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