C++ corrupted file problem please help
- From: "Marvin Hunkin" <startrekcafe@xxxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Thu, 6 Aug 2009 14:32:46 +1000
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hi.
working on a assignment. and wrote a program.
now i navigate to my directory where the file is :
in the command prompt i do:
g++ -o file namethen file name exe.
like for example g++ -o Cash Cash.cpp
and press enter.
it compiles no errors.
but when i try to run the program and Tyep Cash in the command prompt.
the program does not run.
just the file name hangs.
will post the session details for the current session.
as learning to program in c++ using the g cc ++ compiler.
and using text pad to write the code and using the command prompt to compile
and run.
will paste my code and the session details plus the exercise.
if any one can help me out.
that would be gredat.
tried writing this program a couple of times under different file names, but
get the same result.
maybe my logic is flawed.
/*
Program: Cash Register.
File: Cash.cpp
Description: Cash Register Program.
Author: Marvin Hunkin.
Revision: 1.00 05/08/2009 First release.
*/
// iostream is needed for the cout statement.
#include <iostream>
using namespace std;
//Declare functions
float initialise();
float tax(float value);
void total(float value);
int main()
{
//call functions in the main function
initialise();
tax();
total();
} //close main function
float initialise()
{
char item;
int itemNumber;
int counter;
cout<< "Welcome to Marvin's Cash Register Program\n";
//for loop goes here.
for (int counter = 0; counter <=6; counter++)
{
cout<< "Enter a item and then press enter\n";
cin>> item;
cout << "Enter a item number and then press enter\n";
cin>> itemNumber;
} //close for loop
} //close initialise() function
float tax(float value)
{
float tax = 0.1;
char item;
float total = 0;
//if block goes here.
if (item >=10)
{
total = tax * total;
} // close if block
return value;
} // close tax() function
void total(float total)
{
cout << "Total $" << total << endl;
} // close total() function
--------------------------------------------------------------------------------
Session 10
Cohesion and Coupling
--------------------------------------------------------------------------------
Objectives
The purpose of this session is to introduce you to the concept of cohesion
and coupling and what these concepts mean when writing a C++ program.
--------------------------------------------------------------------------------
Last session we looked at how to write a function. This session we are going
to look at how to make better functions. There are a number of objectives
when deciding what to put into a function and what not to put into a
function. Good function design states that functions should be loosely
coupled and be tightly cohesive.
Cohesion
Cohesion is the measure by which the statements within a function relate to
each other. The statements in a function should only perform one task. Most
of the programs that we have written so far have only had one function and
that was the main function. In our examples so far, the main function has
displayed the title information, gathered user input, processed data and
displayed the output. To write good programs, each of our functions should
only perform one task each.
To demonstrate the concept lets use a practical example. We are going to
write a program that keeps track of a persons bank account. With a bank
account we do a number of tasks. We withdraw money, deposit and make a
balance enquiry. The following code does the job but suffers from a lack of
cohesion.
/*
* Program: Cohesion and Coupling example - 1.
* File: cohesCoup1.cpp
* Description: This program is an exercise to demonstrate cohesion in a
program.
* Author: Henry Bush
* Revision: 1.00 2/12/2003 First release.
*/
// iostream is needed for the cout statement.
#include <iostream>using namespace std;
int main()
{
float balance = 0.0;
float amount = 0.0;
char option;
cout << "Welcome to the Bank Account Manager\n\n";
cout << "Enter the account balance: $";
cin >> balance;
cout << "w = withdrawal, d = deposit, b = account balance, x = exit
program" << endl;
cout << "Type in one of the choices from the list above ";
cin >> option;
while(option != 'x')
{
switch(option)
{
case 'b':
cout << "\nThe account balance is: $" << balance << endl;
break;
case 'd':
cout << "Type in the amount that is being deposited: $";
cin >> amount;
balance += amount;
break;
case 'w':
cout << "Type in the amount that is being withdrawn: $";
cin >> amount;
balance -= amount;
break;
case 'x':
exit(0);
break;
default :
cout > option<< " is not a valid value try again ";
break;
} // close switch block
cout << "\nType in one of the choices (w, b, d, x) ";
cin >> option;
} // close while loop
} // close main function
Lets look at the program and see how we can rewrite the program in a much
better manner. The first thing to do is to analyse the tasks that are
performed in the program. Obviously, there are the balance, deposit and
withdrawal tasks, but if we look closer at the program we can see that there
is some beginning programing stuff and a choice task. So if we add these
tasks up we then have 5 tasks and we can write the program with 5 functions.
We can start off by writing the blank functions and declaring them as in the
following
/*
* Program: Cohesion and Coupling example - 1.
* File: cohesCoup1.cpp
* Description: This program is an exercise to demonstrate cohesion in a
program.
* Author: Henry Bush
* Revision: 1.00 2/12/2003 First release.
*/
// iostream is needed for the cout statement.
#include <iostream>using namespace std;
// Declare the functions.
void initialise();
void deposit();
void withdrawal();
void accountbalance();
void input();
int main()
{
} // close main function
void initialise()
{
} // close initialise function
void deposit()
{
} // close deposit function
void withdrawal()
{
} // close withdrawal function
void accountbalance()
{
} // close balance function
void input()
{
} // close input function
At this stage there are no parameters and the return type is void. Lets
start with adding the variables that we need for this program. They were
float balance, float amount and char option, we will add them above the main
function. The reason for this will be explained later this session.
The initialise function is where we are going to display the title, get user
input for the account balance and prime the while loop. Yes, I can already
here you saying that is three things, but for this example it will be OK to
call all of this initialising the program. The function should look like the
following
void initialise()
{
cout << "Welcome to the Bank Account Manager\n\n";
cout << "Enter the account balance: $";
cin >> balance;
cout << "w = withdrawal, d = deposit, b = account balance, x = exit
program" << endl;
cout << "Type in one of the choices from the list above ";
cin >> option;
} // close initialise function
The Deposit function is where we make the deposits so add the code to make
it look like this
void deposit()
{
cout << "Type in the amount that is being deposited: $";
cin >> amount;
balance += amount;
} // close deposit function
And the withdrawal function will have code like this
void withdrawal()
{
cout << "Type in the amount that is being withdrawn: $";
cin >> amount;
balance -= amount;
} // close withdrawal function
The accountbalance function will display the account balance so it will look
like the following
void accountbalance()
{
cout << "\nThe account balance is: $" << balance << endl;
} // close balance function
The input function is where we will input what the users next choice is like
this
void input()
{
cout << "\nType in one of the choices (w, b, d, x) ";
cin >> option;
} // close input function
At this point we only have the main function left and this is where the most
noticeable feature is. The main function now only controls the operation of
the program and lets all of the other functions do the detailed work. The
program will start off with some initialisation and then into a while loop
we will put a switch statement and a call to the input function. Modify your
main function so that it looks like the following
int main()
{
initialise();
while(option!='x')
{
switch(option)
{
case 'b':
accountbalance();
break;
case 'd':
deposit();
break;
case 'w':
withdrawal();
break;
case 'x':
exit(0);
break;
default :
cout << option<< " is not a valid value try again ";
break;
} // close switch block
input();
} // close while loop
} // close main function
One of the big things to note is that main has now become much smaller and
easier to read. Programs that are easy to read are also easier to maintain.
The program should now look like the following
/*
* Program: Cohesion and Coupling example - 1.
* File: cohesCoup1.cpp
* Description: This program is an exercise to demonstrate cohesion in a
program.
* Author: Henry Bush
* Revision: 1.00 2/12/2003 First release.
*/
// iostream is needed for the cout statement.
#include <iostream>using namespace std;
// Declare the functions.
void initialise();
void deposit();
void withdrawal();
void accountbalance();
void input();
float balance = 0.0;
float amount = 0.0;
char option;
int main()
{
initialise();
while(option!='x')
{
switch(option)
{
case 'b':
accountbalance();
break;
case 'd':
deposit();
break;
case 'w':
withdrawal();
break;
case 'x':
exit(0);
break;
default :
cout << option<< " is not a valid value try again ";
break;
} // close switch block
input();
} // close while loop
} // close main function
void initialise()
{
cout << "Welcome to the Bank Account Manager\n\n";
cout << "Enter the account balance: $";
cin >> balance;
cout << "w = withdrawal, d = deposit, b = account balance, x = exit
program" << endl;
cout << "Type in one of the choices from the list above ";
cin >> option;
} // close initialise function
void deposit()
{
cout << "Type in the amount that is being deposited: $";
cin >> amount;
balance += amount;
} // close deposit function
void withdrawal()
{
cout << "Type in the amount that is being withdrawn: $";
cin >> amount;
balance -= amount;
} // close withdrawal function
void accountbalance()
{
cout << "\nThe account balance is: $" << balance << endl;
} // close balance function
void input()
{
cout << "\nType in one of the choices (w, b, d, x) ";
cin >> option;
} // close input function
It is made of a number of small functions that only perform one task each.
This technique makes for programs that are easy to handle as they get
larger. With programs of this size it is hard to justify in your own mind
why you would bother, after all we have nearly doubled the number of lines
of code and have only created the same program. Once your programs reach
hundreds of lines of code you will see the benefits of this type of
technique.
Recapping when you write functions try to put into one function only the
code that performs one task. Sometimes you may need to put statements into a
function that perform more than one task. In these cases try to put tasks
that relate to each other. Another thing to try for is to have your
functions small. Try and have then less than one screen full of text. You
will not always be able to achieve these guides, but if you work towards
them, then you are on the right track.
Coupling.
Where cohesion relates to the function's internal behavior, coupling relates
to how it interacts with the program that it exists in. Functions should be
loosely coupled. By that I mean that a function should not rely on
statements or variables from outside the function.
A well written function should be able to be copied into another program and
work without any changes to the function or the program. If we look at the
example that we have been working on, we can see that each function depends
on the variables that we declared at the beginning of the program. If we
took one of the functions out of this program and placed it into another, we
would have to modify the function or the program to make them work together.
We are going to modify the program again to make the functions loosely
coupled.
Firstly we will move the variable declarations back into the main function.
When they were placed before the main function made them global variables.
Global variables are accessible to all the functions in a program. This is
handy but very dangerous. It is hard to see at this size of program how it
can be a problem. The more parts of a program that can gain access to a
variable, the greater the chance of being altered without realising the
consequences.
To avoid this we use a technique to control the access to variables. By
placing the variable declaration inside a function makes them what are
called local variables. That means that they are only accessible from within
the function. By doing so makes the programs more robust, but it does have
the down side of making the programmer have to think more about the way they
write their programs. The only way to get data into a function is through
the parameter list, and the only way to get data out of a function is
through the return type.
If we look at the initialise function first. We do not need to pass any
variables to the function but we do wish to return the balance entered. So
we make the return type a float. When a function returns a value, the
calling function must accept the value, as in the following
balance = initialise();
Inside this function though we also had the user enter the choice for the
next function. We will move this back to the main function. The deposit
function needs the balance value and we need to return the new balance. So
we need to pass the balance value to the function as a parameter. Within the
function we declare a new variable to hold the amount deposited. After
performing the calculation we need to return the new balance as in the
following
float deposit(float value)
{
float amount = 0.0;
cout << "Type in the amount that is being deposited: $";
cin >> amount;
value += amount;
return value;
} // close deposit function
The withdrawal function will be almost identical to the deposit function
float withdrawal(float value)
{
float amount = 0.0;
cout << "Type in the amount that is being withdrawn: $";
cin >> amount;
value -= amount;
return value;
} // close withdrawal function
The account balance function requires the balance value but does not need to
return anything as in the following
void accountbalance(float value)
{
cout << "\nThe account balance is: $" << value << endl;
} // close balance function
The last function is the input, this function will return a value to the
option variable and does not have to take any parameters.
char input()
{
char inputValue;
cout << "\nType in one of the choices (w, b, d, x) ";
cin >> inputValue;
return inputValue;
} // close input function
Put all together the program will look like this
/*
* Program: Cohesion and Coupling example - 1.
* File: cohesCoup1.cpp
* Description: This program is an exercise to demonstrate cohesion in a
program.
* Author: Henry Bush
* Revision: 1.00 2/12/2003 First release.
*/
// iostream is needed for the cout statement.
#include <iostream>using namespace std;
// Declare the functions.
float initialise();
float deposit(float value);
float withdrawal(float value);
void accountbalance(float value);
char input();
int main()
{
float balance = 0.0;
char option;
balance = initialise();
cout << "w = withdrawal, d = deposit, b = account balance, x = exit
program" << endl;
cout << "Type in one of the choices from the list above ";
cin >> option;
while(option!='x')
{
switch(option)
{
case 'b':
accountbalance(balance);
break;
case 'd':
balance = deposit(balance);
break;
case 'w':
balance = withdrawal(balance);
break;
case 'x':
exit(0);
break;
default :
cout << option<< " is not a valid value try again ";
break;
} // close switch block
option = input();
} // close while loop
} // close main function
float initialise()
{
float value = 0.0;
cout << "Welcome to the Bank Account Manager\n\n";
cout << "Enter the account balance: $";
cin >> value;
return value;
} // close initialise function
float deposit(float value)
{
float amount = 0.0;
cout << "Type in the amount that is being deposited: $";
cin >> amount;
value += amount;
return value;
} // close deposit function
float withdrawal(float value)
{
float amount = 0.0;
cout << "Type in the amount that is being withdrawn: $";
cin >> amount;
value -= amount;
return value;
} // close withdrawal function
void accountbalance(float value)
{
cout << "\nThe account balance is: $" << value << endl;
} // close balance function
char input()
{
char inputValue;
cout << "\nType in one of the choices (w, b, d, x) ";
cin >> inputValue;
return inputValue;
} // close input function
Make sure that you can understand what is happening here in the program.
Cohesion and coupling are important concepts to creating larger workable
programs.
--------------------------------------------------------------------------------
Session 10 Practical Exercise
The practical exercise for this session will be to create a cash register
program that you input the cost of an item, the number purchased and if a
sales tax applies to the item. If a tax does apply to the item, the tax
value will be ten percent of the items cost.
Example
Item Cost Tax Applies? Cost Plus Tax
Bread $2.00 No $2.00
Shirt $20 Yes $22.00
Total $24.00
In the example, the bread costs $2, it does not have sales tax on it, so its
final price is $2. The shirt on the other hand, has a cost of $20, and does
have tax on it, so ten percent of 20 is 2, making the final price of the
shirt $22.00. The program will then calculate the cost of all the items.
This will be in a loop so that a number of different items can be inputed
and when finished the program it will produce a grand total.
If you can complete this exercise without any difficulties then you can
proceed to the next lesson. If you found that you had any problems with this
exercise then contact your instructor about the problems and attach any
working code so that we can discuss where your solutions lay.
After you successfully complete this exercise, remember to send your
completed code into your instructor for assessment.
--------------------------------------------------------------------------------
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