The
"if" Statement
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It's time
to make decisions using the
relational operators. |
The "if"
expression is called a conditional statement (decision
statement). It tests a relationship by using the relational
operators. Based upon the results of these comparisons, decisions are made
as to which statement(s) the program will execute next.
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if (test
condition)
{
block of one;
or more C++ statements;
} |
 |
If you put a
semicolon after the test condition, the "if" statement
will STOP. The block will not be executed. |
The test condition can be any
relational comparison (or logically TRUE) statement and must be enclosed in
parentheses. The block of statements is enclosed in French
curly braces and
are indented for readability. The braces are NOT required if only ONE
statement follows the "if", but it is a good idea to get in the
habit of including them.
The block executes only if the test
condition is TRUE. If the test condition is FALSE, the block is
ignored and execution continues to the next statement following the block.
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Be careful!!!
A careless mistake may go unnoticed.
if (a = 3)
is almost ALWAYS true. The
condition
a = 3
is actually an "assignment statement" (most likely NOT what you
really intended to type), and assignments are consider to
be true for any value other than 0. If the assignment value
is 0, such as
if (a = 0), the
condition is considered false.
whereas:
if (a = = 3)
is true ONLY if the value
stored in a
is the number 3.
This is most likely what you intended to type.
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Examples:
// using a
character literal
if (grade = = 'A')
{
cout<<"Put it on the frig!";
}
|
//
logically true test condition -
// when x is a non-zero value the
// test condition is considered true
if (x)
{
cout<<"Way to go!";
cout<<"The x is not zero!";
} |
// using two variables
if (enemyCount < heroCount)
{
cout<<"The good guys win!";
} |
// using a calculation
if (cost * number = = paycheck)
{
inventory = 0;
} |
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