MCC - CIS162AB

MCC - CIS162AB - C++ Level I
P07 Using the .Net Debugger - 10 points

The purpose of this assignment is to use the Visual C++ .Net debugger tool to figure out why the program below displays some very strange amounts regardless of what is entered by the user. The debugger tool can help programmers find such logic errors. If you find the bug before completing the assignment, don't correct it. Wait until after you have completed all the steps in this assignment.
This assignment should also help you better understand call-by-value, call-by-reference, and the scope of local variables.
The debugger allows the programmer to view the intermediate results stored in variables as the program is executed one step at a time or several lines of code at a time. When executing several lines at a time, the programmer must tell the debugger when to stop by setting a breakpoint on a specific line of code.

This handout walks you through the process of using the debugger tool using a program similar to P05-ex and P06-ex.
Startup Visual C++ and maximize the window size.

Create a new Win32 Console Application projected named P07.
Add a new Text file names output.txt
Add a new C++ Source file named p07.

Startup Mozilla or Internet Explorer.
Go to the course's website and click on P07 Using the Debugger on the course schedule.
Copy and paste the following source code into the source code file p07.cpp.
//P07 Using the Debugger - An Example  Juan Marquez   TR 1:00pm
//
//   This program is used by customers to determine what the cost 
//   of their order would be based on the price and quantity ordered.

#include <iostream>
using namespace std;

//Function Prototypes
void getPrice(double& price);              //call-by-reference
void getQuantity(int quantity);            //call-by-value

double calcCost(double cost, int quantity);
double calcTax(double subtotal, double taxRate);

//Declare the global constants
    const double TAX_RATE = 0.05;

void main()
{
//Declare the local constants
    const double SHIPPING = 10.00;

//Declare local variables
    int  quantity;
    double price, subtotal, salesTax, total;

//Set the decimal point to 2 positions
    cout.setf(ios::fixed);
    cout.setf(ios::showpoint);
    cout.precision(2);

    cout << "P07 - Juan Marquez    TR 1:00pm \n\n";

//Get and validate values
    getPrice(price);
    getQuantity(quantity);

//Calculate amounts
    subtotal = calcCost(price, quantity);
    salesTax = calcTax(subtotal, TAX_RATE);

    total = subtotal + salesTax + SHIPPING;

//Display the results
    cout << endl
         << "Price:    \t" << price     << endl
         << "Quantity: \t" << quantity  << endl
         << "Subtotal: \t" << subtotal  << endl
         << "Sales Tax:\t" << salesTax << " at " << TAX_RATE << endl
         << "Shipping: \t" << SHIPPING  << endl
         << "Total Due:\t" << total     << endl;

    cout << "\nThank you!\n\n";

    return;
} // end of main


//Function Definitions
void getPrice(double& price)
{
    do
    {
        cout << "Enter a value between $5 and $15.00 for the price: ";
        cin >> price;

    } while (price < 5 || price > 15);

    cout << endl;
    return;
}


void getQuantity(int quantity)
{
    do
    {
        cout << "Enter a value between 1 and 50 for the quantity: ";
        cin >> quantity;
		
    }while (quantity < 1 || quantity > 50);
    return;
}


double calcCost(double price, int quantity)
{
    double subtotal;
    subtotal = price * quantity;
    return (subtotal);
}


double calcTax(double subtotal, double taxRate)
{
    double amount;
    amount = subtotal * taxRate;
    return (amount);
}
//end of program
Select Build P07 to compile and link the program.
This should verify that everything was copied correctly.
There should be zero errors and 1 warning. Ignore the warning for now.
Execute the program so that you can see the result of the bug.
Click on Debug on the menu, and scroll down and select Start Without Debugging.
Enter 10 for the price.

A Run-time Debug Error will be displayed regarding the variable quantity.

Click on Ignore to continue.
This message may be displayed up to 3 times during the execution.
Click on Ignore each time.

Enter 10 for the quantity.

Eventually some very strange results should be displayed for quantity and other variables that store values calculated using quantity.
Capture this output and save in output.txt
P07 - Juan Marquez    TR 1:00pm

Enter a value between $5 and $15.00 for the price: 10

Enter a value between 1 and 50 for the quantity: 10

Price:          10.00
Quantity:       -858993460
Subtotal:       -8589934600.00
Sales Tax:      -429496730.00 at 0.05
Shipping:       10.00
Total Due:      -9019431320.00

Thank you!

Press any key to continue
Reminder: Capture this output and save in output.txt
During the debugging process you may want to pause the execution of the program at a particular line code, so that you can observe the values in variables or to watch what happens as each line of code is executed. To cause the program to pause a breakpoint must be inserted.

To set a breakpoint, place the mouse pointer in the margin area that appears as a border at the left edge of the Editor window and click by the line of code you desire the break. A large red dot will display in the margin.

To remove a breakpoint go to the statement that has a breakpoint set, and click on the red dot located in front of the line code.

Set a breakpoint at each of the following statements:

getPrice(price);

getQuantity(quantity);

cout << "Thank you";

on the closing brace } after the return statement in getPrice.

on the closing brace } after the return statement in getQuantity.

Run the program in debug mode.

Click on Debug on the menu, and scroll down and select Start Debugging.
The F5 function key can also be used.

The execution will stop at the first breakpoint, which should be the function call getPrice(price).

The debugger should open three windows.

Top left window is the source code.

The bottom right panel can display the Command Window, Call Stack, Breakpoints, etc.

The bottom left panel can display Auto, Local, and Watch variables (tabs listed at bottom).

Click on the Watch 1 tab to bring it forward.
The Watch 1 panel is where a programmers enter variable names that they want to watch as the variables go in and out of scope and as their values change.
If these windows aren't opened, open the missing window by selecting the menu options:
Debug -> Windows -> Locals
Debug -> Windows -> Watch 1

Set a watch on the variables price, quantity, total, and TAX_RATE as follows:

On the bottom left Watch 1 panel,
click in the first empty cell under the column heading Name.
Type in price.

Click on the next empty cell. Type in quantity.

Click on the next empty cell. Type in total.

Click on the next empty cell. Type in TAX_RATE, which is a global variable.

We will be controlling the execution of the program in debug mode using the function keys F5 and F11.
F5 executes until the next breakpoint or end of program.
F11 steps through the program one statement at time.

Step through getPrice()

Step into the getPrice function using F11.

Since price is the only local variable, the list of local variables should be reduced to price. On the Watch list, only price should have a value, and the others will have a message stating that they were not found (CXX0017: Error: symbol "quantity" not found). However, since TAX_RATE is global variable, its value is still displayed.

Skip to the next breakpoint by pressing F5. Stepping through the cout and cin procedures is very tedious.

Before reaching the next breakpoint, a value for the cin statement in getPrice must be entered.
Enter 10 for the price and press return.
Click on the source code window to bring it to the foreground if it is not visible.

The next breakpoint is at end of the getPrice function.

Notice in the Watch window that price was actually assigned the value of 10.

Press F11 to step back into main.

Notice that the value of 10 was returned to the local variable price defined in main().

Press F11 to get ready to step into getQuantity.

Step through getQuantity()

Press F11 to step into getQuantity.

Click on Continue for the Run-Time Error message.

Before reaching the breakpoint at end of the function, a value for quantity must be entered.
Enter 10 for the quantity and press return.

Click on the source code window to bring it to the foreground if it is not visible.

Notice in the Watch window that the local variable quantity was assigned a value of 10, and that price is now out of scope.

Press F11 to step back into main.

In the variable Watch window we should see that the local variable quantity in main does not have the value of 10 that was entered and visible in getQuantity(). In this case the value entered in the getQuantity function was not returned to main. So the bug is returning the value from the function getQuantity.

What is the error?
How is the value in getQuantity() supposed to get back to main()?
Include your explanation at the bottom of output.txt

Complete debug session

Press F5 to reach the last statement in the program.

Click on Continue for the two additional Run-Time Error messages.

Press F5 to end the debug session.

Any libaries (cout, etc) that you stepped into while in debug will need to have their source code files closed.

The values in variables can be changed during execution while in debug mode.

Press F5 to get the debugger to Go again.

Press F5 to execute the getPrice function.

Click on the console output window to bring it to the foreground if it is not visible.

Enter 10 for the price.

Click on the source code window to bring it to the foreground if it is not visible.

Press F5 to return to main.

Press F5 to execute the getQuantity function.

Click on Continue for the Run-Time Error message.

Click on the console output window to bring it to the foreground if it is not visible.

Enter 10 for the quantity.

Click on the source code window to bring it to the foreground if it is not visible.

At the end of getQuantity, press F11 to return to main.

On the bottom left window (variable window), double click on the value of quantity.

Replace the current value with a 10 and press enter.

Press F5 to complete the calculations.

Even though a value has been entered for quantity, we must still
click on Continue for the two additional Run-Time Error messages.

Notice that the variable now has a valid value.
So, the problem is that quantity is not getting back to main().
The rest of the logic seems to work when quantity has a valid value.

The statement pointer should be at the cout statement that displays thank you.

Click on the console output window on the task bar to see the current output.

Since we manually corrected the quantity, some valid output is now displayed on the output.

Click on the source code window to bring it to the foreground.

Press F5 to end the debugging session.

Complete the assignment.
Correct the bug in the program at this time.

Execute the program again to test the correction.
Capture the correct output and save in output.txt
P07 - Juan Marquez    TR 1:00pm

Enter a value between $5 and $15.00 for the price: 10

Enter a value between 1 and 50 for the quantity: 10

Price:          10.00
Quantity:       10
Subtotal:       100.00
Sales Tax:      5.00 at 0.05
Shipping:       10.00
Total Due:      115.00

Thank you!

Press any key to continue . . .
    
Submit the corrected P07.cpp and output.txt.
Revised: 9/23/2011 - www.mesacc.edu/~marquez/cis162ab/p07_debugger_net.html