Ch6. Art of Programming

Testing techniques for while loops

1. Does the program produce correct results with a set of known inputs? 2. Does the program produce correct results if the sentinal value is the first and only input

enables us to read data easily from a text file

Scanner class

is when we dont know how many times the loop will execute; that is when the loop beings, we dont know how many iterations of the loop will be required.

While loop

In this operation we initialize a total baribale to 0>Each time we input a new value we add the value to the total.When we reach the end of the input, the current value of total is the total for all the input.

accumalation operation

we initialize a total variable to 0 before starting the loop. In the loop body, we add each input value to the total. When the loop completes the current total is the total for all processed input values.

accumulation programming technique

A semicolon that immediately follows the condition indicates

an empty loop body

if you know the number of times a loop will be running you can use

count controlled loop

we intitilize a count varibaale to 0 vefore starting the loop. in the body of the loop we increment the count varibale for each input value that meets out criteria. when the loop completes the count variable contains the number of i tems met out criteria

counting programming technique

type of loop is used for validating input

do while

loop style where the ocndition is tested at the end of the loop

do/while loop

it also posssible to construct a while loop whose conditions never evaluates to false. It results in a

endless or infinite loop

We rely on this to tell us when we have processed all of the data

event

processign of items continues until the end of input is signaled either by a sentinel value or by reaching the end of the file

event controlled looping

when you process each input value until a signal or event tells us that there is no more input

event controlled looping

to avoid generating exceptions when the user types characters other than the data type expected we use

has Next method

the method in the scanner class that reads the info in a file

hasNext

each execution of the loop body is called

iteration

is ran when a loop condition is true

loop body

typically used in a for lop. we set its initial value to 0 in the initialization statement, increment or decrement its value in the loop update statement and check its value in the loop condition

loop counting variable

to make sure the condition have to be false at some point of time you have to include a...

loop update statement

useful when performing multiple operations inside of loops

nested loops

after performing any initialization we attempt to read the first item we call this.. because we feed the condition of the while loop for the first iteration

priming read

is a special input value that signals the end of the items to be processed.

sentinal value

the signal for the end of the input may be a special value that the user enters

sentinel value

if the loop of a condiiton is false the first time it is tested

the body of the for loop is skipped

which loop is designed for the count controlled loop,

the for loop is designed for the count controlled loop that is when the number of iterations is determined before the loop begins.

the important thing to understand about a nested loop

the inner or nested loop executes compelty for each single iteration of the outer loop

can increment or decrement the loop variable by any value

the loop update statement

when you read the next input data

update read because we update the data item in preparation for feeding its value into the condition of the while loop for the next iteration;.

to find the average

we combine accumulation and counting

when the has Next method returns false we know

we have reached the end of the file

Scanning a file we check

whether ther is more data in the file and then read the data

when you want to calculate the sum of a set of values

you use accumulation

it is possible that the whiel loop body is never executed. in that case it is called..

zero iterations