The C Preprocessor Versus the Compiler
One important thing you need to remember is that the C preprocessor is not part of the C compiler.
The C preprocessor uses a different syntax. All directives in the C preprocessor begin with a pound sign (#). In other words, the pound sign denotes the beginning of a preprocessor directive, and it must be the first nonspace character on the line.
The C preprocessor is line oriented. Each macro statement ends with a newline character, not a semicolon. (Only C statements end with semicolons.) One of the most common mistakes made by the programmer is to place a semicolon at the end of a macro statement. Fortunately, many C compilers can catch such errors.
The following sections describe some of the most frequently used directives, such as
TIP
Macro names, especially those that will be substituted with constants, are normally represented with uppercase letters so that they can be distinguished from other variable names in the program.
The C Preprocessor Versus the Compiler
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Exercises : Answer the following Question
To help solidify your understanding of this hour's lesson, you are encouraged to answer the quiz questions and finish the exercises provided in the Workshop before you move to the next lesson.
Question and Answer
Q What are the differences between a union and a structure?
Making Structures Flexible
Making Structures Flexible
The second application of unions is to nest a union inside a structure so that the structure can hold different types of values.
Using Unions
Using Unions
Now let's focus on the applications of unions. Basically, there are two kinds of union applications, which are introduced in the following two sections.
Referencing the Same Memory Location Differently