Chapter 5: Problem 10

Why should you be careful not to place a statement in the body of a for loop that changes the value of the loop's counter variable?

Short Answer

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Provide an example.

Step by step solution

Introduction to 'for' loops in programming

A 'for' loop is a control structure used in programming languages to iterate over a range, sequence of numbers, or elements in an iterable object, such as an array or list. The loop has an initial counter value, a test condition, and an increment or decrement step. The loop repeats until the test condition evaluates to false.

Importance of the loop's counter variable

The loop's counter variable is used to control the number of iterations the loop will execute. It usually gets incremented or decremented after each iteration of the loop. If the loop's counter variable is modified within the loop body, it may result in unpredictable behavior or errors.

Provide an example where changing the loop's counter variable leads to unexpected results

Consider the following Python code example: ```python for i in range(5): print(i) if i == 2: i = 4 ``` In the example above, the programmer intends to skip printing '3' by directly setting the counter variable 'i' to '4' when 'i' is equal to '2'. However, this does not work as intended because the 'for' loop iterates over the range object, regardless of the changes made to its counter variable. Instead of skipping '3', the loop will print: ``` 0 1 2 3 4 ```

Conclusion and best practices

It is essential to be cautious when modifying the loop's counter variable since it can lead to unexpected behavior. Instead of manually changing the counter variable, consider using alternative control structures, such as 'while' loops, or implementing the desired loop control using 'continue' and 'break' statements.

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Why should you be careful not to place a statement in the body of a for loop that changes the value of the loop's counter variable?

Short Answer

Step by step solution

Introduction to 'for' loops in programming

Importance of the loop's counter variable

Provide an example where changing the loop's counter variable leads to unexpected results

Conclusion and best practices

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