Questions tagged [if-statement]

An if statement is a flow control structure in most programming languages that branches execution flow depending on a binary condition, generally evaluated at runtime. If-statements are also commonly known as conditionals.

When using this tag please also include an appropriate language tag, such as e.g. java if your question is language-specific.

Basic Syntax

The if statement has the following syntax:

if <condition>
then
     <statement-1>
else
     <statement-2>

<condition> may be parenthesized (as it is in JavaScript), the keyword then may be omitted (Python, C-like languages, JavaScript and others).

The else section is optional in most languages.

An example if statement in JavaScript:

var myVariable = 100;

if (myVariable >= 20) {
    console.log('My variable is greater than or equal to 20!');
} else {
    console.log('My variable is less than 20!');
}

if-else statements may also be nested, where another if may appear in if statement, and/or in else statement. For example:

if ( number1 > 20 )
   if ( number2 > 50 )
      print('Both numbers satisfy condition')
   else
      print('Second number doesn't satisfy condition')
else
   if( number2 > 50 )
      print('Only Second number satisfies condition')
   else
      print('None of the two numbers satisfy condition')

else+if is used to chain if statements:

if ( number > 20 )
     print('Greater than 20')
else+if ( number > 10 )
     print('Greater than 10')
else
     print('Less than 11')

else+if statements may simply be an else statement followed by an if (e.g else if; done in JavaScript and many C-like languages), or a special keyword such as elif (Python), or elsif (Perl).

As a ternary operator

In C and C-like languages, conditional expressions can take the form of a ternary operator called the conditional expression operator, ?:, which follows this template:

(condition)?(evaluate if condition was true):(evaluate if condition was false)

In Python, if is used explicitly, and the ordering is slightly different:

(evaluate if condition was true) if (condition) else (evaluate if condition was false)

An example of the ternary operator in JavaScript:

var myVariable = 100;

myVariable>20 ? console.log('Greater than 20!') : console.log('Less than or equal to 20!');

See also: condition