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. The answers and hints to the questions and exercises are given in Appendix E, "Answers to Quiz Questions and Exercises."
Quiz

    Given the following function declarations, which ones are functions with a fixed number of arguments, which ones are functions with no arguments, and which ones are functions with a variable number of arguments?
        int function_1(int x, float y);
        void function_2(char *str);
        char *asctime(const struct tm *timeptr);
        int function_3(void);
        char function_4(char c, …);
        void function_5(void);
    Which one of the following two expressions is a function definition?

    int function_1(int x, int y);
    int function_2(int x, int y){return x+y;}

    What is the data type returned by a function when a type specifier is omitted?

    Of the following function declarations, which ones are illegal?
        double function_1(int x, ...);
        void function_2(int x, int y, ...);
        char function_3(...);
        int function_4(int, int, int, int);

Exercises

    Rewrite the program in Listing 15.2. This time use the format specifier %c, instead of %s, to print out the character string of the local time on your computer.
    Declare and define a function, called MultiTwo(), that can perform multiplication on two integer variables. Call the MultiTwo() function from the main() function and pass two integers to MultiTwo(). Then print out the result returned by the MultiTwo() function on the screen.
    Rewrite the program in Listing 15.3. This time, make a function that takes a variable number of int arguments and performs the operation of multiplication on these arguments.
    Rewrite the program in Listing 15.3 again. This time, print out all arguments passed to the AddDouble() function. Does va_arg() fetch each argument in the same order (that is, from left to right) of the argument list passed to AddDouble()?

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The #define and #undef Directives

The #define and #undef Directives

The #define directive is the most common preprocessor directive, which tells the preprocessor to replace every occurrence of a particular character string (that is, a macro name) with a specified value (that is, a macro body).

The C Preprocessor Versus the Compiler

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.

What Is the C Preprocessor?

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.