In computer science, conditional statements are a vital part of a programming language. These statements are requests to the computer to make an execution choice based on a given condition. Computer science, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ... A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. ... A statement is the minimal unit of structuring in imperative programming languages. ... A BlueGene supercomputer cabinet. ...

One form is the If-Then clause, sometimes seen as :

 If (condition) Then (statements) Else (statements) End If 

It works this way - when the computer finds an If (a reserved word), it expects a data comparison, for example, x = 0 and evaluates the condition. If the condition is true, the statement block following the Then (another reserved word) shall be executed, otherwise the execution shall continue in the following statement block. A reserved word is a word which, in some computer programming language, cannot be used as an identifier because it is already used for some grammatical purpose. ... In computer programming, a statement block (or code block) is a section of code which is grouped together, much like a paragraph; such blocks consist of one, or more, statements. ...

Depending on the language, the If may use Then, brackets, and another clause called Else or ElseIf. See parenthesis for an account of the rhetorical concept from which the name of the punctuation mark is derived. ...

There are many other conditional statements in programming languages, however, all of them follow these principles. Other conditional statements include switch statements, case statements and statements with guards. In computer programming, a switch statement is a type of control statement that exists in most modern imperative programming languages (e. ... In computer programming, a switch statement is a type of control statement that exists in most modern imperative programming languages (e. ... In computer programming, a guard is a boolean expression that must evaluate to true if the program execution is to continue in the branch in question. ...

Alternative Syntax

Main article: Ternary operation

Many languages support alternative syntax for if statements: (condition)?(evaluate if condition was true):(evaluate if condition was false).
This is mainly used for in-line if statements that wouldn't be suitable in the place used, for example: In mathematics, a ternary operation is any operation of arity three, that is, that takes three arguments. ...

 //Invalid $var = if(true) { 'foo' } else { 'bar' }; //Valid $var = (true)?'foo':'bar' 

To accomplish the same as the second (correct) line above, using standard if/else construct:

 if (true) { $var = 'foo'; } else { $var = 'bar'; } 

The alternative syntax can also be used inside if statements themselves: that is to say more generally, "The alternative syntax, accomplishing the equivalent of an analogous if/else construct, may be used anywhere an if/else construct may be appropriately used".

See also

• Control flow#Choice
• Conditional branch for a theoretical view
• Pattern matching for another way to make execution choices
• Logical conditional for a more general view of conditionals
• Ternary operation for shorthand syntax provided by most programming languages