C++ Loops: While, Do-While, For

Learning Outcomes

• Students should be able to use while, do-while, and for loops to repeatedly execute statements.
• Students should be able to explain the control flow in loops.
• Students should be able to use Boolean expressions to control loops.
• Students should be able to write nested loops.
• Students should be able to explain the similarities and differences between the three loop types.

Why Repetition is Needed

• Repetition allows repeating an action or a set of actions multiple times.
• C++ provides while, do-while, and for loops to repeat statements until a condition is met.

While Looping Structure

• The while loop repeatedly executes a statement as long as a given expression is true.
• A flowchart of the structure shows an expression, a statement, and a loop.

While Loop

• A while loop repeats a block of code as long as a condition (expression) is true.
• The flowchart and code example illustrate this concisely.
• The loop's body may contain multiple statements.

Tracing While Loop

• The sample code initializes a counter (count) to 0.
• The loop continues as long as the counter is less than 2.
• The output shows how "Welcome to C++" is printed while the counter increments to 2.

Controlling While Loop

• Five types of while loops exist.
• Counter-controlled loops use a counter to control the loop when the number of data items is known.
• Sentinel-controlled loops employ a special value (sentinel) to stop the loop when the number of data items is unknown.
  • The loop continues until the sentinel value is encountered.
• Flag-controlled loops use a Boolean variable (flag) to determine loop termination when a specific condition is met.
• User-controlled loops allow users to control the loop duration.
• End-of-file (EOF)-controlled loops use the end of a file as a sentinel value to stop loops.

Counter-controlled While Loops

• Use a counter to manage the loop when the number of data items is known.
• Initialize the counter to 0, and the loop repeats until the counter equals or surpasses the number of items.
• There's an example code showing how to calculate the average of data scores using a counter-controlled loop.

Sentinel-Controlled While Loops

• Use a sentinel value to stop the loop when the quantity of data isn't known beforehand.
• Useful for processing input from a user where the amount is uncertain.
• This method continues until the sentinel value is entered.
• An example in the presentation demonstrates a program to find the total number of points scored by a soccer team. This example uses the value -1 as the sentinel.

Flag-Controlled While Loops

• A Boolean flag controls the loop.
• The loop continues until the flag changes to a certain value.
• This is helpful for processes where you want to repeatedly ask for user input until a certain input is given.

EOF-Controlled While Loops

• Use EOF (End-of-File) as a signal to terminate a loop.
• Common in cases where you read data from a file until the end is encountered.
• The loop stops automatically when encountering EOF.

Do-While Loop

• The do-while loop guarantees the code block within the loop executes at least once.
• The condition is checked at the end of the loop, continuing execution as long as it's true.

For Loop

• The for loop is used when the number of iterations is known beforehand.
• It has three components: initialization, condition, and update, all separated by semicolons.
• The presentation illustrates the structures of both the flowchart and the C++ code of a for loop.

Nested For Loop

• Nested for loops enable looping within another loop.
• It allows processes involving multiple iterations with various variables.

Other Statements Related to Looping

• break: Terminates any loop, either the innermost (nested loop) or all loops.
• continue: Skips the remainder of the current loop iteration and goes to the next iteration or test expression, based on the loop type.

Comparing For and While Loops

• for loops are preferred when the loop's iterations are predetermined.
• while loops excel when the number of iterations is unknown or depends on conditions.
  • do-while loops ensures the code within the block executes at least once.

Specific examples

• Code snippets demonstrating different looping patterns and their outputs are included in the slides.

This quiz focuses on the different types of loops in C++: while, do-while, and for. Students will learn to execute statements repeatedly and understand control flow in loops. Additionally, the quiz covers nested loops and the use of Boolean expressions for controlling loop execution.