G.5. Autos Window

G.5. Autos Window The Autos window displays the variables used in the previous statement executed (including the return value of a function, if there is one) and the variables in the next statement to execute. 1. Setting breakpoints. Set breakpoints at lines 14 and 22 in main by clicking in the margin indicator bar. 2. Using the Autos window. Start the debugger by selecting Debug > Start. When the debugger enters break mode at line 14, open the Autos window (Fig. G.22) by selecting Debug > Windows > Autos. Since we are just beginning the program's execution, the Autos window lists only the variables in the next statement that will execute—in this case, the account1 object, its value and its type. Viewing the values stored in an object lets you verify that your program is manipulating these variables correctly. Notice that account1 contains a large negative value. This value, which may be different each time the program executes, is account1's uninitialized value. This unpredictable (and often undesirable) value demonstrates why it is important to initialize all C++ variables before they are used. Fig. G.22. Autos window displaying the state of account1 object. 3. Using the Step Over command. Select Debug > Step Over to execute line 14. The Autos window updates the value of account1's balance data member (Fig. G.23) after it is initialized. The value of balance is displayed in red to indicate that it just changed. Fig. G.23. Autos window displaying the state of account1 object after initialization. 4. Continuing execution. Select Debug > Continue to execute the program until the second breakpoint at line 22. The Autos window displays uninitialized local variable withdrawalAmount (Fig. G.24), which has a large negative value. Fig. G.24. Autos window displaying local variable withdrawalAmount. 5. Entering data. Select Debug > Step Over to execute line 22. At the program's input prompt, enter a value for the withdrawal amount. The Autos window updates the value of local variable withdrawalAmount with the value you entered (Fig. G.25). Fig. G.25. Autos window displaying updated local variable withdrawalAmount. 6. Stopping the debugger. Select Debug > Stop Debugging to end the debugging session. Remove all remaining breakpoints.