This is visually ugly but valid code. You do have to observe some rules. In particular, in C and C++ you can’t put a space, tab, or carriage return in the middle of an element such as a name, nor can you place a carriage return in the middle of a string. Here are examples of what you can’t do:
int ma in() // INVALID -- space in name
re
turn 0; // INVALID -- carriage return in word
cout << "Behold the Beans
of Beauty!"; // INVALID -- carriage return in string
(However, the
Tokens and White Space in Source Code
The indivisible elements in a line of code are called
Figure 2.3. Tokens and white space.
return0; // INVALID, must be return 0;
return(0); // VALID, white space omitted
return (0); // VALID, white space used
intmain(); // INVALID, white space omitted
int main() // VALID, white space omitted in ()
int main ( ) // ALSO VALID, white space used in ( )
C++ Source Code Style
Although C++ gives you much formatting freedom, your programs will be easier to read if you follow a sensible style. Having valid but ugly code should leave you unsatisfied. Most programmers use styles similar to that of Listing 2.1, which observes these rules:
• One statement per line
• An opening brace and a closing brace for a function, each of which is on its own line
• Statements in a function indented from the braces
• No whitespace around the parentheses associated with a function name
The first three rules have the simple intent of keeping the code clean and readable. The fourth helps to differentiate functions from some built-in C++ structures, such as loops, that also use parentheses. This book alerts you to other guidelines as they come up.
C++ Statements
A C++ program is a collection of functions, and each function is a collection of statements. C++ has several kinds of statements, so let’s look at some of the possibilities. Listing 2.2 provides two new kinds of statements. First, a
Listing 2.2. carrots.cpp
// carrots.cpp -- food processing program
// uses and displays a variable
#include
int main()
{
using namespace std;
int carrots; // declare an integer variable
carrots = 25; // assign a value to the variable
cout << "I have ";
cout << carrots; // display the value of the variable
cout << " carrots.";
cout << endl;
carrots = carrots - 1; // modify the variable
cout << "Crunch, crunch. Now I have " << carrots << " carrots." << endl;
return 0;
}
A blank line separates the declaration from the rest of the program. This practice is the usual C convention, but it’s somewhat less common in C++. Here is the program output for Listing 2.2:
I have 25 carrots.
Crunch, crunch. Now I have 24 carrots.
The next few pages examine this program.
Declaration Statements and Variables
Computers are precise, orderly machines. To store an item of information in a computer, you must identify both the storage location and how much memory storage space the information requires. One relatively painless way to do this in C++ is to use a
int carrots;
This statement provides two kinds of information: the type of memory storage needed and a label to attach to that storage. In particular, the statement declares that the program requires enough storage to hold an integer, for which C++ uses the label int. The compiler takes care of the details of allocating and labeling memory for that task. C++ can handle several kinds, or types, of data, and the int is the most basic data type. It corresponds to an integer, a number with no fractional part. The C++ int type can be positive or negative, but the size range depends on the implementation. Chapter 3 provides the details on int and the other basic types.
