Chapter 4 Flashcards by Peter Glynn

What is a loop in programming?

A program construct that repeatedly executes a set of statements while a condition is true

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What is the loop body?

The statements executed repeatedly within a loop

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What is an iteration?

One complete execution of the loop body

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What real-world example illustrates looping?

Driving around the block until a baby falls asleep

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What determines whether a loop continues or exits?

The loop expression’s evaluation (true = continue, false = exit)

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What is a sentinel value?

A special input value that signals the end of data processing

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What type of loop uses a sentinel value?

Loops that process input until a termination condition is met

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What causes an infinite loop?

Forgetting to update a loop control variable or using the wrong loop expression

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How do you prevent infinite loops?

Ensure loop variables are properly updated within the loop body

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What is the basic structure of a while loop?

while expression is true, execute loop body, then recheck expression

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What common task uses a loop to process lists?

Computing sums, averages, counts, or finding maximum/minimum values

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In the baby asleep example, what represents the loop decision point?

Checking if the baby is awake

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What happens when a loop’s expression evaluates to false?

Execution proceeds to the statement after the loop

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When does a loop’s expression get evaluated?

Before each iteration of the loop body

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What is a common mistake when writing loops?

Using the opposite expression than intended or forgetting input updates

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What is a loop that never stops called?

An infinite loop

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What is the purpose of initializing variables before a loop?

To ensure the loop body operates on correct starting values

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What pattern allows processing unknown input amounts?

Using a sentinel value that marks the end of input

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What is the output of this code with inputs 2, 4, 1, -1?

sum = 7 (sum adds inputs until -1 is encountered)

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Why do we often use “val > -1” in loop expressions?

To exclude sentinel values like -1 from calculations

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What happens if you forget to update the input within a loop?

The loop may become infinite or behave incorrectly

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What does this loop accomplish: counting negative numbers?

It counts how many negative values are in a list

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How can you find the maximum in a list using a loop?

Compare each input to current max and update if larger

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What is wrong with initializing max to 0 for unknown lists?

If all list values are negative, max will be incorrect

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Why is initializing max with the first input preferred?

It ensures comparisons start with actual list data

What is the loop expression for "iterate while x is less than 100"?

x < 100

How do you iterate until a value equals 15?

Use the expression: while value != 15

What is an example of looping N times?

A loop with initialization, expression, and update controlling exact repetitions

What are the three essential parts of an N-times loop?

Initialization, loop expression, and update statement

What is the common pattern for looping 10 times?

i = 0; while i < 10; i = i + 1

How can loops create flexible output sequences?

By adjusting the loop variable's initialization, expression, or update step

What does the following loop output: i = 5; while i <= 15; i = i + 3?

Outputs: 5 8 11 14

What is a nested loop?

A loop placed inside the body of another loop

What is the difference between inner and outer loops?

The inner loop completes all iterations for each outer loop iteration

What task is well-suited for nested loops?

Creating tables, grids, or processing 2D data

What does this nested loop output: for row = 1 to 2, for col = 1 to 3?

Outputs: 2 3 4 3 4 5

What is the total number of inner loop executions if outer runs 4 times, inner runs 6?

24 total inner loop executions

In a nested loop, when does the inner loop variable reset?

At the start of each outer loop iteration

How can you output a multiplication table using nested loops?

Outer loop for rows, inner loop for columns, output row * column

How can nested loops create patterns like triangles?

Outer loop controls rows, inner loop controls items per row

What causes an infinite loop in this code: while x == 0?

If x is never updated within the loop body

What is a do-while loop?

A loop that executes the body first, then checks the condition

When is a do-while loop preferred?

When the loop must execute at least once (e.g., menu systems)

What is the main difference between while and do-while loops?

do-while guarantees at least one execution; while may skip entirely

Where is the condition evaluated in a do-while loop?

After the loop body executes

What happens if the condition is false from the start in a do-while loop?

The loop body still executes once

What is a for loop's structure?

Initialization; expression; update — all at the top of the loop

When is a for loop preferred?

When the number of iterations is known beforehand

How can you convert a for loop to a while loop?

Separate initialization before, use expression in while, update inside body

What is the order of execution in a for loop?

Initialization → condition check → body → update → repeat

What does this for loop output: for i = 0; i < 3; i++?

Outputs: 0 1 2

What happens if you modify the loop control variable inside a for loop?

It may cause incorrect iterations or infinite loops

What does this loop output: for num = 10; num >= 2; num -= 2?

Outputs: 10 8 6 4 2

What is the purpose of descriptive loop variable names?

Improves readability and code clarity

What happens in this while loop: i = 0; while i < 5; i++?

Outputs: 0 1 2 3 4

What expression creates an infinite loop: while x != 0, but x never changes?

The loop never exits because x stays constant

What task is best for a while loop?

Processing input until a termination condition is met

What task is best for a for loop?

Executing a known number of iterations

What happens if you omit updating the loop variable?

The loop may become infinite or logically incorrect

What causes off-by-one errors in loops?

Incorrect initialization or improper expression boundaries

What is output by this loop: i = 0; while i < 4; sum += 3; i++?

Outputs: sum = 5, 8, 11, 14 (if sum starts at 5)

Why is initializing a loop variable before the loop important?

Ensures correct starting values for loop execution

What does this code output: value = 100; while value >= 10; value /= 2?

Outputs: 100 50 25 12

How can you output multiples of 7 from 14 to 70?

Initialize at 14, loop while ≤ 70, increment by 7 each iteration

What task requires nested loops for full processing?

Creating a grid, pattern, or 2D table

What does the bar chart nested loop accomplish?

Prints lines of asterisks representing numeric values

How many times does the inner loop run if outer runs 3 times, inner runs 5?

15 total inner loop executions

What loop type guarantees at least one iteration?

do-while loop

What is the correct expression to iterate while x is not equal to 10?

x != 10

How do you loop exactly 25 times?

Initialize i = 0; loop while i < 25; increment i by 1

How can loops process lists of unknown length?

Use a sentinel value to mark the end of input

What is the role of a sentinel value?

To signal the end of an input list

What happens in Euclid's GCD algorithm when numA % numB = 0?

The loop terminates; numB contains the GCD

How can you process student grades until -1 is entered?

Loop while grade != -1, process each grade inside the loop

Why is Euclid's algorithm efficient for finding GCD?

It reduces the numbers quickly through division

What is the loop expression to output even numbers up to 50?

i = 2; while i ≤ 50; i += 2

How do you create a multiplication table using loops?

Nested loops: outer for rows, inner for columns, output product

What prevents infinite loops during input processing?

Always get new input within the loop body

What expression continues a loop while userNum is not -1?

userNum != -1

Why might a for loop be better than a while loop for array processing?

The number of iterations is pre-determined by array size

How can you loop down from 40 to -10 in steps of -5?

Initialize at 40, loop while ≥ -10, decrement by 5 each iteration

What is the importance of loop variable updates?

Prevents infinite loops and controls loop progression

When would you use a while loop over a for loop?

When the number of iterations depends on dynamic conditions

How can you validate user input with a loop?

Loop until valid input is received, checking conditions inside the loop

What does this loop do: while x < 1000; x *= 2?

Finds the first power of 2 greater than or equal to 1000

Why use nested loops for 2D arrays?

To process rows and columns systematically

What happens to complexity with additional nested loops?

It increases, often exponentially with each level

How do you create Pascal's triangle with loops?

Nested loops: outer controls rows, inner calculates combinations

What loop type is ideal for menu systems?

do-while loop, to guarantee menu displays at least once

How can you find both max and min in a list?

Loop through all values, update max and min as needed

What causes off-by-one errors in for loops?

Incorrect expression boundaries like i <= N instead of i < N

Why is it important to use descriptive loop variable names?

Improves code clarity and understanding of loop purpose

What loop pattern generates every 3rd element of a list?

Initialize index = 0; loop while < size; increment by 3 each time

Chapter 4 Flashcards

(93 cards)