Why Do I Get an IndexError in My \'for i in ar\' Loop When Summing List Values?

IndexError in "for i in ar" Loop: Understanding the Iteration

When attempting to sum the values of a list using a for loop, one may encounter an IndexError, TypeError, or incorrect results. This error arises due to an incorrect usage of the list index.

Consider the following code:

<code class="python">def sumAnArray(ar):
    theSum = 0
    for i in ar:
        theSum = theSum + ar[i]
    return theSum</code>

Here, we intend to loop through the list and accumulate the values in theSum. However, the code triggers an IndexError because i represents each element of the list, not its index.

To correctly loop through the list and access its elements, one should modify the code to:

<code class="python">def sumAnArray(ar):
    theSum = 0
    for i in ar:
        theSum = theSum + i
    return theSum</code>

Alternatively, one can use a range to iterate over valid list indices:

<code class="python">def sumAnArray(ar):
    theSum = 0
    for i in range(len(ar)):
        theSum = theSum + ar[i]
    return theSum</code>

These modifications ensure that i represents a valid index within the list, preventing the IndexError and enabling correct calculation of the sum.

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