Page 66 - Programming Microcontrollers in C

Functions 51

actly this operation for us. When a C program encounters a break,
it jumps to the end of the current block. Therefore, the breaks
following the executable statements above will cause the program to
jump out of the executing sequence and return to get the next charac­
ter from the input stream.
When all options have been exhausted without a match, the state­
ments following the default line will be executed. It is not necessary
to have a default line.

EXERCISES
1. Write a program that counts the number of lines, words, and char­
acters in an input stream.

2. Extend the program from the exercise above to calculate the per­
centage usage of each character in the alphabet.

3. A prime number is a number that cannot be evenly divided by any
number. For example, the numbers 1, 2, and 3 are all prime num­
bers. Write a program that will calculate and print out the first 200
prime numbers.

Write this program without the use of either a modulo or a divide
operation.

Functions
The function is the heart of a C program. In fact, any C program
is merely a function named main. The purpose of a function is to
provide a mechanism to allow a single entry of a code sequence that
is to be repeated many times. A function is the most reusable element
in the C language. Properly written and debugged functions can be
collected into a program when needed. Therefore, the use of func­
tions will allow the programmer to write smaller programs and it is
not necessary to rewrite common functions that are used often.
A function can have many arguments or none whatsoever. Func­
tion arguments are contained in parentheses following the function
name. The values of the arguments are the parameters needed to
execute the function. A function can return a value, or perhaps it will
not have a return value. An example of a function that returns a value
is getchar() which returns a character from the input stream.