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Engineering LibreTexts

21.7: Looping and Counting

  • Page ID
    16990
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    The following program counts the number of times the letter a appears in a string:

    word = 'banana'
    count = 0
    for letter in word:
        if letter == 'a':
            count = count + 1
    print count
    

    This program demonstrates another pattern of computation called a counter. The variable count is initialized to 0 and then incremented each time an a is found. When the loop exits, count contains the result—the total number of a’s.

    Exercise \(\PageIndex{1}\)

    Encapsulate this code in a function named count, and generalize it so that it accepts the string and the letter as arguments.

    Exercise \(\PageIndex{2}\)

    Rewrite this function so that instead of traversing the string, it uses the three-parameter version of find from the previous section.


    This page titled 21.7: Looping and Counting is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

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