Page 63 - Programming Microcontrollers in C

48 Chapter 1 Introduction to C

has the normal printf arguments. Note however that the string is
not confined to one line. C compilers will not allow a string to be
split among several lines in a program. However, an ANSI C compli­
ant compiler will cause two adjacent strings to be concatenated into
a single string, so the above code will compile without error.

Break, continue, and goto

These commands will cause a C program to alter its program
flow. If a break statement is encountered, the program will exit the
loop in which it is executing. Break can be used to exit for, while,
do-while, and switch statements. An example of the use of the
break statement is shown in the next section.
The continue statement causes the next iteration of a for,
while, or a do while loop to be started. In the case of the for
statement, the last argument is executed, and control is passed to the
beginning of the for loop. For both the while and the do-while,
the argument of the while statement is tested immediately, and the
program proceeds according to the result of the test.
The break statement is seen frequently, and the continue
statement is rarely used. Another statement that is even more rarely
used is the goto. In C, the programmer can create a label at any
location by typing the label name followed by a colon. If it is neces­
sary, the goto <label> can be used to transfer control of the
program from one location to another. In general, C provides enough
structured language forms that the use of the goto <label> se­
quence will rarely be needed. One place where the goto can be
used effectively is when the program is nested deeply and an error is
detected. In such a case, the goto statement is an effective means of
unwinding the program from a deep loop to an outer loop to process
the error. In general, you should avoid goto statements whenever
possible.
That said, there is an excellent alternative to a goto. The reach
of a goto is limited to the function in which it is defined. In fact, the
reach should probably be confined to the block in which it is de­
fined. Since new variables can be defined at the beginning of any
block, undefined behavior can be introduced when a goto branches
into a block where new variables have been defined. Also, you can
introduce undefined behavior when you branch out of a block where