Professional

Using blocks to group statements
Notice that the syntax of the if statement shown earlier specifies a single statement after the
if (booleanExpression) and a single statement after the else keyword. Sometimes, you’ll want to
perform more than one statement when a Boolean expression is true. You could group the statements
inside a new method and then call the new method, but a simpler solution is to group the
statements inside a block. A block is simply a sequence of statements grouped between an opening
brace and a closing brace.
In the following example, two statements that reset the seconds variable to 0 and increment the
minutes variable are grouped inside a block, and the entire block executes if the value of seconds is
equal to 59:
int seconds = 0;
int minutes = 0;
...
if (seconds == 59)
{
seconds = 0;
minutes++;
}
else
{
seconds++;
}
Important If you omit the braces, the C# compiler associates only the first statement
(seconds = 0;) with the if statement. The subsequent statement (minutes++;) will not be
recognized by the compiler as part of the if statement when the program is compiled.
Furthermore, when the compiler reaches the else keyword, it will not associate it with the
previous if statement; instead, it will report a syntax error. Therefore, it is good practice to
always define the statements for each branch of an if statement within a block, even if a
block consists of only a single statement. It might save you some grief later if you want to
add additional code.
A block also starts a new scope. You can define variables inside a block, but they will disappear at
the end of the block. The following code fragment illustrates this point:
if (...)
{
int myVar = 0;
... // myVar can be used here
} // myVar disappears here
else
{
// myVar cannot be used here
...
}
// myVar cannot be used here
CHAPTER 4 Using decision statements 93