Question

What output will be produced when the following lines are executed (assuming the lines are embedded in a complete and correct program with the proper include directives)? cout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; cout.setf(ios::showpos); cout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; cout.unsetf(ios::showpos); cout.setf(ios::left); cout << "*" << setw(5) << 123 << "*" << setw(5) << 123 << "*" << endl;

Short answer

Answer: The output produced will be: ``` * 123*123* * +123*+123* *123 *123 * ```

Step-by-step solution

Part 1: Initial Output

First, let's analyze the output produced by the first 2 lines of code: ``` cout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; ``` These lines will output a '*' character, followed by a field of width 5 containing the number 123. The '*' character will be placed after the number as well. Next, the number 123 will be output again without any padding, followed by the '*' character and a line break. Output: ``` * 123*123* ```

Part 2: Output with ShowPos Flag

Now let's analyze the output after setting the `ios::showpos` flag: ``` cout.setf(ios::showpos); cout << "*" << setw(5) << 123 << "*" << 123 << "*" << endl; ``` Here, the flag `ios::showpos` is set, which adds a positive sign to the number. Then, similar to the first part, a '*' character is followed by a field of width 5 containing the number 123 but with a positive sign this time. Again, a '*' character is placed after the number, and the number 123 is output again (with the positive sign due to the showpos flag), followed by the '*' character and a line break. Output: ``` * +123*+123* ```

Part 3: Output with Left Alignment and No ShowPos Flag

Finally, let's analyze the output after unsetting the `ios::showpos` flag and setting the `ios::left` flag: ``` cout.unsetf(ios::showpos); cout.setf(ios::left); cout << "*" << setw(5) << 123 << "*" << setw(5) << 123 << "*" << endl; ``` Here, the flag `ios::showpos` is unset, which removes the positive sign from the number. The flag `ios::left` is set, which aligns the number to the left within the field. This time, a '*' character is followed by a field of width 5 with a left-aligned number 123. A '*' character is placed after the number, and the number 123 is output again within a field of width 5 and left-aligned, followed by the '*' character and a line break. Output: ``` *123 *123 * ``` So, the complete output will be: ``` * 123*123* * +123*+123* *123 *123 * ```

Key concepts

iostream library

The iostream library is a fundamental part of C++ that allows you to perform input and output operations. It is part of the C++ standard library and includes facilities such as standard input (cin), standard output (cout), and error messages (cerr). These objects are instances of iostream classes and are used to read and write data to streams like the console or files.

For instance, cout is often used to display output on the screen. In combination with IO manipulators, you can control output formatting to align data, set the precision, and insert special characters in an easy-to-read and organized manner. Understanding the iostream library is crucial for formatting output in C++.

setw function

The setw function stands for 'set width' and is used to define a specific width for the next data item that you're going to insert into the output stream. This is particularly useful for formatting output. You must include the header file <iomanip> to use it.

Here's an example of how setw is used:
cout << setw(10) << 77 << endl;
This line will output the number 77 with enough leading spaces to make the total length 10 characters. If no character is specified to fill the extra space, it defaults to spaces. setw only affects the next output item; once the item is printed, the stream's width resets.

ios::showpos

The ios::showpos manipulator is used to force the output stream to display a '+' sign in front of positive numbers, making it clear that they are indeed positive. This can be very helpful when you want to emphasize the sign of the number for clarity or formatting purposes.

To enable this feature, you use the setf function on your output stream object like so:
cout.setf(ios::showpos);
And to disable it, you can use the unsetf function like this:
cout.unsetf(ios::showpos);
Once the ios::showpos flag is set, it will remain in effect until explicitly turned off, and it will apply to every positive numerical output following its activation.

ios::left

The ios::left manipulator is another formatting tool used to align the output to the left of the given field width set by setw. By default, if the number of characters is less than the width specified, the output is right-aligned and the extra space is filled up with spaces on the left. When the ios::left flag is set, the additional space will go to the right of the data instead, ensuring it aligns to the left edge of the field.

To use ios::left, similar to showpos, you use the setf function:
cout.setf(ios::left);
This setting is particularly useful in creating neatly-formatted tables and aligning columns of text or numbers.