If there is a constant appearing in several places in your program, it's a good idea to associate a symbolic name to the constant, and then use the symbolic name to replace the constant throughout the program. There are two advantages to doing so. First, your program will be more readable. Second, it's easier to maintain your program. For instance, if the value of the constant needs to be changed, find the statement that associates the constant with the symbolic name and replace the constant with the new one. Without using the symbolic name, you have to look everywhere in your program to replace the constant. Sounds great, but can we do this in C?
Well, C has a special program called the C preprocessor that allows you to define and associate symbolic names with constants. In fact, the C preprocessor uses the terminology macro names and macro body to refer to the symbolic names and the constants. The C preprocessor runs before the compiler. During preprocessing, the operation to replace a macro name with its associated macro body is called macro substitution or macro expansion.
You can put a macro definition anywhere in your program. However, a macro name has to be defined before it can be used in your program.
In addition, the C preprocessor gives you the ability to include other source files. For instance, we've been using the preprocessor directive #include to include C header files, such as stdio.h, stdlib.h, and string.h, in the programs throughout this book. Also, the C preprocessor enables you to compile different sections of your program under specified conditions.
What Is the C Preprocessor?
Related Items
The continue Statement
The continue Statement
The break Statement
The break Statement
You can add a break statement at the end of the statement list following every case label, if you want to exit the switch construct after the statements within a selected case are executed.
The switch Statement
The switch Statement
Nested if Statements
Nested if Statements
As you saw in the previous sections, one if statement enables a program to make one decision. In many cases, a program has to make a series of decisions. To enable it to do so, you can use nested if statements.
The if-else Statement
The if-else Statement