More Loops

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count-controlled loop must posses 3 elements:

1. It must initialize a counter variable to begin with 2. Test the initialization variable with a counter variable by comparing it to the maximum value, and terminate when reached. 3.Update the counter variable during each iteration, usually by increment it.

What three steps are taken when a file is used by a program

1. Open the file 2. Process the File 3. Close the File

Programs that calculate the total of a series of numbers typically use 2 elements:

1. A loop that reads each number in the series 2. A variable that accumulates the total of the numbers as they are read.

to read large files use a...

loop

read position

marks the location of the next byte that will be read from the file

To get the total number of iterations of a nested loop

multiply the number of iterations of all thee loops

num -= 1;

num = num - 1;

postfix mode

num++

An example of opening a file for output writing

ofstream outputFile; outputFile.open("Employees.txt");

header ofstream

output file stream. you create an object of this data type when you want to create a file and write data to it

Example and format of writing a string literal to a file

outputFile << "I love C++ programming\n";

Example and format of writing a string literal and the contens of a variable to a file

outputFile << "Price: " << Price << endl;

A common way to accidentally create an infinite while loop that makes the program look like it is lost in space

place a semicolon after the while () like: while ();

do-while loop

post test loop - its expression is tested after each iteration

programming read

provides the first value for the loop to test. it is entered just before the loop takes place

when using multiple statements in the initialization or update expression

separate values with a comma

Two general ways to access data stored in a file:

sequential and random access files

file-name extensions

short sequences of characters that appear at the end of the filename preceeded by a period

how to fave a user define the start and stop of the for loop

store their input in to a min and max variable and initialize num = min and go num <+ max

2 types of files

text and binary

a while loop will terminate when

the expression is found false

loop header

the first line of the for loop

postfix mode causes

the increment to happen after the value of the variable is used in the expression

prefix mode causes

the increment to happes after the value of the variable is used in the expression

input validation

the process of inspecting data given to a program by the user and determining if it is valid.

reading data

the process of retrieving data from the file

writing data

the process of saving data to a file

without a colse of the file

the program will have an error after a loop

If no braces are included in the loop, the while loop will only execute:

the statement immediately following it

two backslashes are needed

to represent one backslash in a string literal

Any non zero value is evaluated as

true

in order to use multiple statements in the test expression

use && or ||

A common mistake in while loops causing the test expression to assign a number to the variable instead of testing whether the variable i eqal to a number

using = instead of ==

a variable in the RAM

when a piece of data is read from a file, it is copied from the file to...

the first byte in the file

when an input file is opened its read position is initially set to ...

variables

when data is read from a file, the data flows from the file stream object that is associated with the file, into ...

file

when s program needs to store date for later use, it writes the data in a ....

format of while loop

while (expression) statement;

example using >> as a boolean expression in a while loop

while (inputFile >> number) If there are no more items to be read from the file the expression returns false

when the >> operator extracts data from the file it reads pieces of data separated by

whitespace characters (spaces, tabs or newlines).

random access file aka direct access file

works like a cd. you can jump directly to any piece of data in the file without reading the data that becomes before it.

sequential access file

you access data from the beginning of the file to the end of it. To get to one point of the file, you must pass through everything preceding it. Works like a cassette tape.

Process the file

Data is read from or written to the file

#include <fstream>

The header file in code for reading and writing files

Accumulator

The variable used to keep the running total

opening an input file

allows the program to read data from the fiel

user-controlled loop

allows the user to decide the number of iterations

test expression

an expression that controls the execution of the loop - as long as this expression is true the body of the loop will repeat

file stream object

an object that is associated wit a specific file and provides a way for a program to work with that file. - stream aka stream of data

Difference between do and do-while loop

because do-while is post-test loop and does not test the expression until it has completed an iteration, it will always do at least one iteration even if false, whereas the while is a pre-test loop

two types of loops

conditional loops and count controlled loops

text file

contains data that has been encoded as text using a scheme such as ASCII orUnicode

binary file

contains data that has not been converted to text.

infinite loop

continues to repeat until the program is interrupted.

Example of a while loop repeating and asking the user to enter a number between 1-100 until a number in the correct range is entered

cout << "enter #"; cin >> num; while (num<1 || num >100) { count << "enter a num in corect range"; cin >> num; }

Open the file

creates a connection between the file and the program

opening an output file

creates the file on the disk and allows the program to write data to it

decrement

decrease by one

control structures

direct the flow of a program

Close the file

disconnects the file from the program after the program is finsihed

format of do-while loop

do statement; while (expression);

iteratiion

each repetition of a loop

counter

a variable that is regularly incremented or decremented each time a loop iterates

Good times to use the for loop

Ideal in situations where the exact number of iterations is unknown.

prefix mode

++num

Good times to use a do-while loop

Ideal in situations where you always want the loop to iterate t least once. Good choice for repeating a menu.

2 things to happen before data can be written to or read from a file

1. a file stream object must be created 2. The file must be opened and linked to the file stream object

2 important parts of the while loop

1. an expression is tested for true and false, and 2. a statement or block that is repeated as long as the expression is true

c = a * b++ a=2, b=5

10

c = a * ++b a=2, b=5

11

Nested loop

A loop inside of another loop

Count-Controlled Loops

A loop that repeats a specific number of times - such as sales amounts for each month in a year must iterate 12 times

fstream

File stream. Objects of this data type can be used to open files for reading, writing, or both.

Good times to use a while loop

In situations where you do not want the loop to iterate if the condition is false from the beginning, such as, validating input that has been read and reading lists of data terminated by a sentinel value.

for loop is a pretest or posttest loop?

Pre-test - as long as the expression is true, the body of the loop will repeat

A loop keeps a running total because it

accumulates the total as it reads each number in the series

loop

a control structure that causes a statement or a group of statements to repeat

input file

a file that data is read from

output file

a file that data is written to

The for loop is ideal for performing

a known number of iterations

Sentinel

a special value that marks the end of a list of values. It cannot be mistaken as a member of the list and signals that there are no more values to be entered. When a user enters it the loop terminates.

A running total

a sum of numbers that accumulates with each iteration of a loop.

Conditional Loop

executes as long as a particular condition exists - such as a menu that executes as long as the input is valid

update expression

executes at the end of each iteration, usually increments the variable

filenames

files on a disk are identified by their...

Format of the For loop

for (initialization; test; update) statement;

what would make the for loop not terminate when you expect it to

if a statement in the body loop also modifies the counter variable

use a if statement to determine if the file opened correctly

if(inputFile)

how to define a file stream object and open a file in one statemetn

ifstream inputFile("customers.txt"); ofstream outputFile("Employees.txt");

Define an ifstream object and name it inputFile

ifstream inputFile;

code for creating a filestream object and linking the file to be open to the file stream object in order to open a file for input

ifstream inputFile; inputFile.open("Customers.txt")

when to use a for loop instead of a do while or while loop

in any situation that clearly requires an initialization, uses a false statement to stop the loop, and requires and update to occur at the end of the iteration.

file stream object in memory

in order for a program to work with a file on the computers disk, the program must create a ...

increment

increase by one

initialization expression

initialize a counter variable into its string value

header ifstream

input file stream. You create an object of this data type when you want to open an existing file and read data from it

example reading input from a file into the variable name

inputFile >> name;

the file stream object's close member function to call to close a file:

inputFile.close();

Call the inputFile object's member function and pass the string "Customers.txt" as an argument

inputFile.open("Customers.txt")

when a variable is defined in a for loop

it is not accesable outside the loop


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