if
Statement (C)
The if
statement controls conditional branching. The body of an if
statement is executed if the value of the expression is nonzero. The syntax for the if
statement has two forms.
selection-statement
:
if (
expression
)
statement
if (
expression
)
statement
else
statement
In both forms of the if
statement, the expressions, which can have any value except a structure, are evaluated, including all side effects.
In the first form of the syntax, if expression
is true (nonzero), statement
is executed. If expression
is false, statement
is ignored. In the second form of syntax, which uses else
, the second statement
is executed if expression
is false. With both forms, control then passes from the if
statement to the next statement in the program unless one of the statements contains a break
, continue
, or goto
.
The following are examples of the if
statement:
if ( i > 0 )
y = x / i;
else
{
x = i;
y = f( x );
}
In this example, the statement y = x/i;
is executed if i
is greater than 0. If i
is less than or equal to 0, i
is assigned to x
, and f( x )
is assigned to y
. The statement forming the if
clause ends with a semicolon.
When nesting if
statements and else
clauses, use braces to group the statements and clauses into compound statements that clarify your intent. If no braces are present, the compiler resolves ambiguities by associating each else
with the closest if
that lacks an else
.
if ( i > 0 ) /* Without braces */
if ( j > i )
x = j;
else
x = i;
The else
clause is associated with the inner if
statement in this example. If i
is less than or equal to 0, no value is assigned to x
.
if ( i > 0 )
{ /* With braces */
if ( j > i )
x = j;
}
else
x = i;
The braces surrounding the inner if
statement in this example make the else
clause part of the outer if
statement. If i
is less than or equal to 0, i
is assigned to x
.