Loop Structures

Name: Loop Structures
Author: John Crabtree

Learn the best uses for different loop structures

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Course: On-Demand

In Python, the most basic kind of loop is called an name definite loop. We use the while keyword in a conditional expression, such that, if the expression evaluates to true, we will execute the loop body that is indented inside of the while. This is very similar to an if, or if else structure. The statements that are indented belong to the loop, and are called the loop body. Now I'm going to add a input statement that is going to prompt the end user to Enter to continue. And notice, I don't have a variable on the left-hand side, and so I'm not interested in whatever they type in, I'm just using this to pause the execution of my program. So as long as I continue to hit Enter, we're going to stay inside the loop body. In fact, there is nothing that causes us to exit this loop, because true will not change. So therefore, I need to use Ctrl + C, hold down Ctrl and press the C button on your keyboard in order to interrupt. And, please keep that in mind because, if you work with while loops long enough, you will inevitably run into this problem where you execute a loop, and it will run forever, unless you do something like hit Ctrl + C. Now sometimes, we want to use a variable, and we want to stay inside the loop as long as the value meets some kind of condition like being greater than or equal to zero. And, in this case, we could prompt the end user for a new value. And in fact, it's a good programming practice to make sure that your condition involves some kind of variable that will change within the loop body. Otherwise, you're risking having an infinite loop. And so I'm going to prompt for a number, transform the string that's returned from input into an integer, and then check that value to see if it's greater than zero. So now I have a loop that, as long as I enter a positive number, or something that's zero, I will continue, but as soon as I enter a negative number, it will end. Sometimes we can use letters instead of numbers to control our loop. For example, I can create a variable called keep_going. And, my condition here would be, as long as my new variable is equal to 'y', remember I'm comparing the variable on the left to the literal on the right, as long as this is true, I'm going to continue to see stay in my loop. And so, I don't need to convert this to an integer. And, I need to use that variable, because once again, I want to make sure that my expression involves some kind of variable that's going to change within the loop body. And, I'm going to also change my prompt to make a little more sense. So this version uses a variable that's a string instead of a number.

Beginner Provider : John Crabtree 4 Lessons · 16m in Arabic, German, English, Spanish, French, Portuguese, Chinese

Course Description

Loops are presented in these lessons, beginning with the while loop. The use of counting with while loops is demonstrated followed by a discussion of the range object and its use in for loops. The two different loop types are then compared and contrasted with a discussion of which style to use and why.

LEARNING OBJECTIVES:

What You'll Learn

Understand the purpose and best uses for a while loop
Recognize that a while loop is indefinite and depends on end-user input
Use counting techniques with while loops
Apply the range() object within for loops
Recognize that a for loop is definite and best used when the number of iterations is known
Compare and contrast while loops and for loops to choose the right style

Key Takeaways

A while loop is indefinite and depends on the end user inputting information.
A for loop is definite and should be used when you know how many times your program needs to loop.
The range object is introduced and used together with for loops.
The course compares and contrasts the two loop types and discusses which style to use and why.

Frequently Asked Questions

What does this course cover?

It presents loop structures, beginning with the while loop, demonstrates counting with while loops, discusses the range object and its use in for loops, and compares while and for loops to explain which style to use and why.

What is the difference between a while loop and a for loop in this course?

The course explains that a while loop is indefinite and depends on the end user inputting information, while a for loop is definite and should be used if you know how many times your program needs to loop.

What lessons are included?

The lessons are Indefinite Loops, Counting with While Loops, For Loops and Range(), and While vs. For Loops.

What skills does this course build?

It covers Code Structure, Control Loops, Data Structures, Loop Unrolling, Nested Loops, and Programming Concepts.