Conditional Statement
Are statements that check an expression then may or may not execute a statement or group of statement depending on the result of the condition.
Types of Conditional Statement
The If Statement
The If-Else Statement
The Nested-If Statement
The If-Else-If Ladder
The Switch Statement
The Nested Switch Statement
The If Statement
The general form of the If statement is:
if ( expression)
statement;
Expression is relational or Boolean expression that evaluates to a TRUE (1) or False (0) value.
Statement may either be a single C statement or a block of C statements.
The general form of the If statement with block statement is:
if ( expression)
{
statement_sequence;
}
In an if statement, if the expression evaluates to TRUE (1), the statement or the block of statements that forms the target of the if statement will be executed. Otherwise, the program will ignore the statement or the block of statements.
The If-Else statement
The general form of the if-else statement is:
If (expression)
statement_1;
else
statement_2;
Where:
– If and else are reserved words
– Expression is relational or Boolean expression that evaluates to a TRUE (1) or False (0) value.
– Statement_1 and statement_2 may either be a single C statement or a block of c statements.
If an if-else statement, if the expression is TRUE (1), the statement or block of statement after the if statement will be executed; otherwise, the statement or block of statement in the else statement will be executed.
Note: Only the code associated with the if or the code that is associated with the else executes, never both.
Nested-If statement
One of the most confusing aspects of the if statement in any programming language is nested ifs. A nested if is an if statement that is the object of either an if or else.
This is sometimes referred to as “an if within an if.”
The reason that nested ifs are so confusing is that it can be difficult to know what else associates with what if.
Fortunately, C provides a very simple rule for resolving this type of situation.
In C, the else is linked to the closest preceding if that does not already have an else statement associated with it.
The if-else-if Ladder
A common programming construct in C is the if-else- if ladder.
In an if-else-if ladder statement, the expression are evaluated from the top downward.
As soon as a true condition is found, the statement associated with it is executed and the rest of the ladder will not be executed. If none of the condition is true, the final else is executed.
The final else acts as a defaults condition. If all other conditions are false, the last else statement is performed.
If the final else is not present, then no action takes place.
Note: The final else is optional, you may include this part if needed in the program or you may not include if not needed.
The switch statement
The switch statement is a multiple-branch decision statement.
In a switch statement, a variable is successively tested against a list or integer or character constants.
If a match is found, a statement or block of statement is executed.
The default part of the switch is executed if no matches are found.
According to Herbert Schildt (1992), there are three important things to know about switch statements:
l 1. The switch differs from if statements in such a way that switch can only test fro equality whereas if can evaluate a relational or logical expression.
l 2. No two case constants in the same switch can have identical values. Of course, a switch statement enclosed by an outer switch may have case constant that are the same.
l 3. If character constants are used in the switch, they are automatically converted to their integer values.
Note: The break statement is used to terminate the statement associated with each case constant. It is a C keyword which means that at that point of execution, you should jump to the end of the switch statement by the symbol }.
