Details of a C Function
Functions are the building blocks of C programs. Besides the standard C library functions, you can also use some other functions made by you or another programmer in your C program. In Chapte 02 you saw the main() function, as well as two C library functions, printf() and exit(). Now, let's have a closer look at functions.
As shown in Figure 3.1, a function consists of six parts: the function type, the function name, arguments to the function, the opening brace, the function body, and the closing
Figure 3.1. The anatomy of a function in the C language. brace.
The six parts of a function are explained in the following sections.
Determining a Function's Type
The function type is used to signify what type of value a function is going to return after its execution. In Hour 2, for instance, you learned that the default function type of main() is integer. You also learned how to change the function type of main() to void so that the main() function does need to return any value.
In C, int is used as the keyword for the integer data type. In the next hour, you'll learn more about data types.
Giving a Function a Valid Name
A function name is given in such a way that it reflects what the function can do. For instance, the name of the printf() function means "print formatted data."
There are certain rules you have to follow to make a valid function name. The following are examples of illegal function names in C:
| Illegal Name | The Rule |
| 2 (digit) | A function name cannot start with a digit. |
| * (Asterisk) | A function name cannot start with an asterisk. |
| + (Addition) | A function name cannot start with one of the arithmetic signs that are reserved C keywords. |
| . (dot) | A function name cannot start with .. |
| total-number | A function name cannot contain a minus sign. |
| account'27 | A function name cannot contain an apostrophe. |
Some samples of valid function names are as follows:
- file2send
- big_score
- _fast_download
- relation2
- sample2copy
- abcdef
