Programming Loops

Questions and Answers

Repeating an operation of any kind

Sentinel loop

Iteration

The old value is replaced with the new value Signup and view all the answers

To terminate the loop Signup and view all the answers

Counting loop Signup and view all the answers

Loops Signup and view all the answers

It is garbage collected Signup and view all the answers

To count how many times a loop has executed Signup and view all the answers

Evaluate the expression, then execute the body, then repeat Signup and view all the answers

It is a pre-test loop Signup and view all the answers

The body of the loop is skipped and control passes out of the loop Signup and view all the answers

To exit the loop early Signup and view all the answers

Implicitly Signup and view all the answers

A loop that executes indefinitely Signup and view all the answers

They are often confused with each other Signup and view all the answers

Study Notes

Loops are the second major part of control flow, after branching.
A loop lets you repeat a block of code (the loop body), and each repetition is known as an iteration.

There are two kinds of loops:
- Sentinel loops, which have a sentinel value that triggers the termination of the looping, and are preferred when you don’t know how many iterations the problem will take.
- Counting loops, which are used when you know a-priori how many times you wish the loop body to repeat.

A loop control variable (LCV) is a variable that is used to control the loop.
In Python, while loops handle LCVs explicitly, and for-each loops handle LCVs implicitly.
In other languages, C-style for loops manage LCVs explicitly.

An infinite loop is a loop that has no termination condition, causing it to repeat indefinitely.

In most languages, you can exit a loop early using:
- Break: exits the loop completely.
- Continue: skips the current iteration and continues with the next iteration.
- Return: exits the loop and returns a value from a function.

To debug loops, you can use various techniques such as:
- Printing out variables and expressions to see their values.
- Using a debugger to step through the code.

The syntax for a while loop is: while expression: statement(s).
A while loop is a pre-test loop, which means that the condition is checked before the body of the while loop is executed.
If the condition is false, the body of the loop is not executed.