The Conditional Operators in C
The conditional operators ? and : are sometimes called ternary operators since they take three arguments. In fact, they form a kind of foreshortened if-then-else. Their general form is,
expression 1 ? expression 2 : expression 3
What this expression says is: “if expression 1 is true (that is, if its value is non-zero), then the value returned will be expression 2,otherwise the value returned will be expression 3”. Let us understand this with the help of a few examples:
(a)
int x, y ;
scanf ( “%d”, &x ) ;
y = ( x > 5 ? 3 : 4 ) ;
This statement will store 3 in y if x is greater than 5, otherwise it will store 4 in y.
The equivalent if statement will be,
if ( x > 5 )
y = 3 ;
else
y = 4 ;
(b)
char a ;
int y ;
scanf ( “%c”, &a ) ;
y = ( a >= 65 && a <= 90 ? 1 : 0 ) ;
Here 1 would be assigned to y if a >=65 && a <=90 evaluates to true, otherwise 0 would be assigned.
Point to be Noted:
- It’s not necessary that the conditional operators should be used only in arithmetic statements. This is illustrated in the following examples:
Ex.:
int i ;
scanf ( “%d”, &i ) ;
( i == 1 ? printf ( “Amit” ) : printf ( “All and sundry” ) ) ;
Ex.:
char a = ‘z’ ;
printf ( “%c” , ( a >= ‘a’ ? a : ‘!’ ) ) ;
- The conditional operators can be nested as shown below.
int big, a, b, c ;
big = ( a > b ? ( a > c ? 3: 4 ) : ( b > c ? 6: 8 ) ) ;
- Check out the following conditional expression:
a > b ? g = a : g = b ;
This will give you an error ‘Lvalue Required’. The error can be overcome by enclosing the statement in the : part within a pair of parenthesis. This is shown below:
a > b ? g = a : ( g = b ) ;
In absence of parentheses the compiler believes that b is being assigned to the result of the expression to the left of second =. Hence it reports an error.
The limitation of the conditional operators is that after the ? or after the : only one C statement can occur. In practice rarely is this the requirement. Therefore, in serious C programming conditional operators aren’t as frequently used as the if-else.
Summary
- There are three ways for taking decisions in a program. First way is to use the if-else statement, second way is to use the conditional operators and third way is to use the switch
statement. - The default scope of the if statement is only the next statement. So, to execute more than one statement they must be written in a pair of braces.
- An if block need not always be associated with an else block.However, an else block is always associated with an if statement.
- If the outcome of an if-else ladder is only one of two answers then the ladder should be replaced either with an else-if clause or by logical operators.
- && and || are binary operators, whereas, ! is a unary operator.
- In C every test expression is evaluated in terms of zero and non-zero values. A zero value is considered to be false and a non-zero value is considered to be true.
- Assignment statements used with conditional operators must be enclosed within a pair of parenthesis.
