Fundamentals of Breakpoints

Introduction

A breakpoint is a line in the code where you want the execution to suspend. The reason you use a breakpoint is to examine what happens in your application when execution reaches that point.

Practical Learning: Introducing Breakpoints

1. Start Microsoft Visual Studio
2. Create a new Console App named WattsALoan2
3. In the Solution Explorer, right-click Program.cs -> Rename
4. Type LoanEvaluation (to get LoanEvaluation.cs) and press Enter
5. Change the document as follows:

   using static System.Console;
   
   Title = "Watts' A Loan?";
   
   WriteLine("This application allows you to evaluate a loan.");
   WriteLine("To proceed, enter the following values.");
   WriteLine("=---------------------------------------------=");
   
   Write("Enter the principal:        ");
   double principal = double.Parse(ReadLine()!);
   
   Write("Enter the interest rate:    ");
   double interestRate = double.Parse(ReadLine()!);
   
   Write("Enter the number of months: ");
   int periods = int.Parse(ReadLine()!) / 12;
   
   double iRate   = interestRate / 100;
   double interestAmount = principal * iRate * periods;
   double futureValue    = principal + interestAmount;
   
   WriteLine("===============================================");
   WriteLine("Loan Summary");
   WriteLine("=---------------------------------------------=");
   WriteLine("Principal:                  {0:F}", principal);
   WriteLine("Interest Rate:              {0:P}", iRate);
   WriteLine("Period For:                 {0} months", periods);
   WriteLine("Interest Amount:            {0:F}", interestAmount);
   WriteLine("Future Value:               {0:F}", futureValue);
   WriteLine("==============================================");

6. To start debugging, on the main menu, click Debug -> Start Debugging
7. Enter the values requested and press Enter after each:

   This application allows you to evaluate a loan.
   To proceed, enter the following values.
   =---------------------------------------------=
   Enter the principal:        3725.85
   Enter the interest rate:    8.765
   Enter the number of months: 36
   ===============================================
   Loan Summary
   =---------------------------------------------=
   Principal:                  3725.85
   Interest Rate:              876.50%
   Period For:                 36 months
   Interest Amount:            979.71
   Future Value:               4705.56
   ==============================================
   
   Press any key to close this window . . .

Creating a Breakpoint

A breakpoint is a line (or section) of code where you want the execution to pause until you, as the developer or application tester, decide to continue. To have a breakpoint, you must create it. To create a breakpoint, first identify the line of code where you want to add it. Then:

• In the left margin corresponding to the interested line, click
• On the main menu, click Debug and click Toggle Breakpoint
• Right-click the interested line of code, position the mouse on Breakpoint, and click Insert Breakpoint
• Click anything on the line and press F9

A breakpoint is represented by a red circular button:

After creating a breakpoint, when code executes and reaches that line, it would pause and let you know by drawing a right-pointing yellow button:

Practical Learning: Creating and Using a Breakpoint

1. In the Code Editor, click the margin on the left side of "double futureValue = principal + interestAmount"

   

2. On the main menu, click Debug -> Start Debugging.
   Notice that the DOS window displays

   

   If necessary, click the Locals tab to show the contents of its window
3. In the DOS window, enter the value of the principal as 6255.75 and press Enter
4. For the interest rate, type 9.725 and press Enter
5. For the number of months, type 48 and press Enter
   The focus moves back to Microsoft Visual Studio:

   

   Notice the values in the Locals window.
   Position the mouse on each variable in the Code Editor and observe the value
6. To continue debugging, on the main menu of Microsoft Visual Studio, click Debug and click Continue:

   This application allows you to evaluate a loan.
   To proceed, enter the following values.
   =---------------------------------------------=
   Enter the principal:        6255.75
   Enter the interest rate:    9.725
   Enter the number of months: 48
   ===============================================
   Loan Summary
   =---------------------------------------------=
   Principal:                  6255.75
   Interest Rate:              9.73%
   Period For:                 48 months
   Interest Amount:            2433.49
   Future Value:               8689.24
   ==============================================
   
   To automatically close the console when debugging stops, enable Tools->Options->Debugging->Automatically close the console when debugging stops.
   Press any key to close this window . . .

Creating Breakpoints

Usually, you want to test various sections of your code for different reasons or goals. As a result, you can create as many breakpoints as you want. When debugging, the debugger would stop at each breakpoint. You can then continue when you have examined code at the selected breakpoint.

Practical Learning: Creating and Using Breakpoints

1. In the Code Editor, click anywhere on the double iRate = interestRate / 100; line to give it focus
2. On the main menu of Microsoft Visual Studio, click Debug and click Toggle Breakpoint
3. In the Code Editor, right-click anywhere on the WriteLine("Interest Amount: {0:F}", interestAmount); line -> Breakpoint -> Insert Breakpoint:

   

4. To start debugging, press F5
5. When requested, enter the value of the principal as 18225.45 and press Enter
6. For the interest rate, type 6.815 and press Enter
7. For the number of months, type 60 and press Enter.
   The focus moves to Microsoft Visual Studio

   

   Notice the values in the Locals window.
   Position the mouse on each variable in the Code Editor and observe the value
8. To continue debugging, press F5.
   Notice the values in the Locals window.
   Position the mouse on each variable in the Code Editor and observe the value

   

9. To continue, on the Standard toolbar, click the Continue button (or press F5) continuously until the DOS window displays the loan summary:

   his application allows you to evaluate a loan.
   To proceed, enter the following values.
   =---------------------------------------------=
   Enter the principal:        18225.45
   Enter the interest rate:    6.815
   Enter the number of months: 60
   ===============================================
   Loan Summary
   =---------------------------------------------=
   Principal:                  18225.45
   Interest Rate:              6.82%
   Period For:                 5 months
   Interest Amount:            6210.32
   Future Value:               24435.77
   ==============================================
   
   Press any key to close this window . . .

Stepping Into Breakpoints

You can combine the Step Into and/or the Step Over feature with breakpoints. That is, you can examine each code line after line until you get to a specific line. This allows you to monitor the values of variables and see their respective values up to a critical section. To do this, first create one or more breakpoints, then proceed with steps of your choice.

Practical Learning: Stepping to Breakpoints

1. Make sure the previous breakpoints are still set.
   To start debugging, on the main menu, click Debug -> Step Into.
   Make sure you can see the Code Editor, the Locals window, and the DOS window

   

2. To continue debugging, on the Debug toolbar of Microsoft Visual Studio, click the Step Into button continuously (6 times) until the DOS window receives focus
3. When the value of the principal is requested, type 6535.85 and press Enter.
   The focus moves to Microsoft Visual Studio

   

4. To continue debugging, on the Debug toolbar, click the Step Into button twice
5. When the interest rate is requested, type 7.625 and press Enter.
   Notice the values in the Locals window
6. To continue, on the Debug toolbar, click the Step Into button twice
7. When the number of months is requested, type 48 and press Enter.
   The focus moves to Microsoft Visual Studio.
   Notice that the first breakpoint is reached

   

8. Press F11 to continue:

   

9. Press F11 to continue:

   

10. Press F11 to continue:

    

11. Press F11 continuously. Watch how focus moves to the lines in the Code Editor. Also watch the values in the Locals window:

    This application allows you to evaluate a loan.
    To proceed, enter the following values.
    =---------------------------------------------=
    Enter the principal:        6535.85
    Enter the interest rate:    7.625
    Enter the number of months: 48
    ===============================================
    Loan Summary
    =---------------------------------------------=
    Principal:                  6535.85
    Interest Rate:              7.62%
    Period For:                 48 months
    Interest Amount:            1993.43
    Future Value:               8529.28
    ==============================================
    
    Press any key to close this window . . .

12. Press A to close the DOS window and return to your programming environment

A Breakpoints Window

Introduction

Breakpoints are some types of objects and must be managed. For example, you can create breakpoints as we saw in previous sections. You can also delete them or create new ones in different sections of your code.

A Window for Breakpoints

To assist you in using and managing breakpoints, Microsoft Visual Studio provides a special window: The Breakpoints window. To get the Breackpoints window, you should first start a debugging operation. The Breakpoints window usually appears in the bottom (-right) section of Microsoft Visual Studio.

When in a Breakpoint-Less Session

When you start a debugging session, if there is no breakpoint in your project, a Breakpoints window would display but it would be empty:

Otherwise, if you had first created some breakpoints, their list would display in the Breakpoints window.

Managing Breakpoints

Introduction

Remember that each breakpoint shows a button in the margin of its line in the Code Editor. In the Breakpoints window, each breakpoint is represented by a row in the list:

Removing a Breakpoint

At any time, such as after using a breakpoint, you can remove it. To delete a breakpoint:

• In the Code Editor, click the breakpoint in the margin
• Right-click the line that has the breakpoint, position the mouse on Breakpoint, and click Delete Breakpoint
• Click anything on the line that has the breakpoint:
  • On the main menu of Microsoft Visual Studio, click Debug and click Toggle Breakpoint
  • Press F9
• In the Breakpoints window:
  • Click the record of the undesired breakpoint. On the toolbar of the Breakpoints window, click the Delete the Selected Breakpoints, or press Alt+F9 followed by D:

    

  • Right-click the undesired breakpoint and click Delete:

    

Practical Learning: Deleting a Breakpoint

• In the Code Editor, click each breakpoint in the margin to remove it

Deleting all Breakpoints

Remember that you can create more than one breakpoint. If you have more than one breakpoint in your code, execution would pause at each one of them. At any time, you can remove one or all breakpoints. To delete all breakpoints, on the main menu, click Debug -> Delete all Breakpoints.

Disabling a Breakpoint

Remember that when you are debugging your code, if you had created some breakpoints, code execution would stop (or break) at each breakpoint. If you already know what is supposed to happen on a breakpoint, we saw that you can delete such a breakpoint. Sometimes, you may want to conduct a debugging operation that must ignore a certain breakpoint, in which case you don't yet want to remove such a breakpoint. In that case, you can disable a breakpoint instead of deleting it. When a breakpoint is disabled:

• In the Code Editor, the breakpoint appears with an empty circle:

  

• In the Breakpoints window, the breakpoint appears with an unchecked check box and an empty circle:

  

To disable a breakpoint:

• In the Code Editor, right-click the button of the breakpoint in the margin and click Disable Breakpoint
• Right-click the line that has the breakpoint, position the mouse on Breakpoint, and click Disable Breakpoint
• Click anything on the line that has the breakpoint. Then, press Ctrl + F9
• In the Breakpoints window, click the record of the undesired breakpoint. On the toolbar of the Breakpoints window, click the Disable All Breakpoints Matching Current Search Criteria button

Practical Learning: Ending the Lesson

• Close Microsoft Visual Studio

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