• An application sometimes needs to perform repetitive actions like: Summing Numbers(Averages) Entering Multiple Data Entries Prompting the User Till the Correct Value is

Entered A shopping list(scanning through the shopping

list and getting the items 1 by one until the list is down and then you leave)

 

• When a program repeatedly runs a set of statements it is referred to as a loop, iteration or repetition structure.

• There are several types of looping structures:

While Loops Do-While Loops For Loops

Counter Controlled Loops

Condional Loops

• Loops are similar to conditionals because they run on a true/false value set. The loop continuously runs while the condition is true and terminates when it is false.

• Loops can be run for a desired length or until a flag terminates them

Great technique to reuse code and therefore limit the amount of statements a program needs. Reusing the same conditional arguments for testing instead of posting hundreds.

True False

Question: How many statements are needed for the following?Ask the same question 100 timesStore the answer in a variableCheck whether the answer is one of two

answers

Question: How many statements are needed if we loop the code?

• A While Loop is a loop that executes 0 or more times before terminating.

• Pre-conditional loop

Code: Creating a While Loop:

while (condition statement):statement1

statement2 

Debugging Techniques: Setup a counter to keep track of the number of times a

loop runs Set up a counter to count if an event is occurring or the

number of times it occurs Output values each time a loop executes

num = eval(input(“Enter a number less than 10:”))

while (number >= 10):print(“Invalid Entry!”)num = eval(input(“Enter a number less than

10:”))

Counter: a variable that is incremented or decremented each time a loop repeats

Can be used to control execution of the loop (also known as the loop control variable)

Must be initialized before entering loop