C++ Primer Plus

The cout.put() member function provides an alternative to using the << operator to display a character. At this point you might wonder why there is any need for cout.put(). Much of the answer is historical. Before Release 2.0 of C++, cout would display character variables as characters but display character constants, such as 'M' and 'N', as numbers. The problem was that earlier versions of C++, like C, stored character constants as type int. That is, the code 77 for 'M' would be stored in a 16-bit or 32-bit unit. Meanwhile, char variables typically occupied 8 bits. A statement like the following copied 8 bits (the important 8 bits) from the constant 'M' to the variable ch:

char ch = 'M';

Unfortunately, this meant that, to cout, 'M' and ch looked quite different from one another, even though both held the same value. So a statement like the following would print the ASCII code for the $ character rather than simply display $:

cout << '$';

But the following would print the character, as desired:

cout.put('$');

Now, after Release 2.0, C++ stores single-character constants as type char, not type int. Therefore, cout now correctly handles character constants.

The cin object has a couple different ways of reading characters from input. You can explore these by using a program that uses a loop to read several characters, so we’ll return to this topic when we cover loops in Chapter 5, “Loops and Relational Expressions.”

char Literals

You have several options for writing character literals in C++. The simplest choice for ordinary characters, such as letters, punctuation, and digits, is to enclose the character in single quotation marks. This notation stands for the numeric code for the character. For example, an ASCII system has the following correspondences:

• 'A' is 65, the ASCII code for A.

• 'a' is 97, the ASCII code for a.

• '5' is 53, the ASCII code for the digit 5.

• ' ' is 32, the ASCII code for the space character.

• '!' is 33, the ASCII code for the exclamation point.

Using this notation is better than using the numeric codes explicitly. It’s clearer, and it doesn’t assume a particular code. If a system uses EBCDIC, then 65 is not the code for A, but 'A' still represents the character.

There are some characters that you can’t enter into a program directly from the keyboard. For example, you can’t make the newline character part of a string by pressing the Enter key; instead, the program editor interprets that keystroke as a request for it to start a new line in your source code file. Other characters have difficulties because the C++ language imbues them with special significance. For example, the double quotation mark character delimits string literals, so you can’t just stick one in the middle of a string literal. C++ has special notations, called escape sequences, for several of these characters, as shown in Table 3.2. For example, \a represents the alert character, which beeps your terminal’s speaker or rings its bell. The escape sequence \n represents a newline. And \" represents the double quotation mark as an ordinary character instead of a string delimiter. You can use these notations in strings or in character constants, as in the following examples:

Table 3.2. C++ Escape Sequence Codes

char alarm = '\a';

cout << alarm << "Don't do that again!\a\n";

cout << "Ben \"Buggsie\" Hacker\nwas here!\n";

The last line produces the following output:

Ben "Buggsie" Hacker

was here!

Note that you treat an escape sequence, such as \n, just as a regular character, such as Q. That is, you enclose it in single quotes to create a character constant and don’t use single quotes when including it as part of a string.

The escape sequence concept dates back to when people communicated with computers using the teletype, an electromechanical typewriter-printer, and modern systems don’t always honor the complete set of escape sequences. For example, some systems remain silent for the alarm character.

The newline character provides an alternative to endl for inserting new lines into output. You can use the newline character in character constant notation ('\n') or as character in a string ("\n"). All three of the following move the screen cursor to the beginning of the next line:

cout << endl;    // using the endl manipulator

cout << '\n';    // using a character constant

cout << "\n";    // using a string

You can embed the newline character in a longer string; this is often more convenient than using endl. For example, the following two cout statements produce the same output:

cout << endl << endl << "What next?" << endl << "Enter a number:" << endl;

cout << "\n\nWhat next?\nEnter a number:\n";

When you’re displaying a number, endl is a bit easier to type than "\n" or '\n', but when you’re displaying a string, ending the string with a newline character requires less typing:

cout << x << endl;    // easier than cout << x << "\n";