Statements

 

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C++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (C++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until C++17*)
noexcept specifier (C++11)
Exceptions
throw-expression try block	handler
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
const/volatile decltype (C++11) auto (C++11)	constexpr (C++11) consteval (C++20) constinit (C++20)
Storage duration specifiers
Initialization
Default-initialization Value-initialization Zero-initialization Copy-initialization Direct-initialization	Aggregate initialization List-initialization (C++11)   Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (C++11)
User-defined (C++11)
Utilities
Attributes (C++11)
Types
typedef declaration
Type alias declaration (C++11)
Casts
Implicit conversions static_cast const_cast	Explicit conversions dynamic_cast reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
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Virtual function override specifier (C++11)   final specifier (C++11)	explicit (C++11) static
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Default constructor Copy constructor Move constructor (C++11)	Copy assignment Move assignment (C++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (C++11)
Miscellaneous
Inline assembly	History of C++

 

Statements

Labels

label : statement

Expression statements

expression ;

Compound statements

{ statement... }

Selection statements

if

switch

Iteration statements

while

do while

for

range for (C++11)

Jump statements

break

continue

return

goto

Declaration statements

declaration ;

Try blocks

try block

Transactional memory

synchronized, atomic_commit, etc (TM TS)

 

Statements are fragments of the C++ program that are executed in sequence. The body of any function is a sequence of statements. For example:

int main()
{
    int n = 1; // declaration statement
    n = n+1; // expression statement
    std::cout << "n = " << n << '\n'; // expression statement
    return 0; // return statement
}

There are seven types of statements:

1) expression statement;

2) compound statement;

3) selection statement;

4) iteration statement;

5) jump statement;

6) declaration statement;

7) try block statement.

Label

Any statement can be labeled, by providing a label followed by a colon before the statement itself:

attr(optional) identifier : statement	(1)
attr(optional) case constexpr : statement	(2)
attr(optional) default : statement	(3)

1) Target for goto.

2) Case label in a switch statement.

3) Default label in a switch statement.

An attribute sequence attr may appear just before the label (in which case it applies to the label), or just before any statement itself, in which case it applies to the entire statement. A statement may carry multiple labels. Labels (and only labels) have function scope. Labels are ignored by unqualified lookup: a label can have the same name as any other entity in the program.

Expression statement

An expression followed by a semicolon is a statement.

attr(optional) expression(optional) ;	(1)

attr(C++11)	-	optional sequence of any number of attributes
expression	-	an expression

Most statements in a typical C++ program are expression statements, such as assignments or function calls.

An expression statement without an expression is called a null statement. It is often used to provide an empty body to a for or while loop. It can also be used to carry a label in the end of a compound statement.

Compound statement

A compound statement or block is a brace-enclosed sequence of statements.

attr(optional) { statement...(optional) }	(1)

When one statement is expected, but multiple statements need to be executed in sequence (for example, in an if statement or a loop), a compound statement may be used:

if (expr) // start of if-statement
{ // start of block
  int n =1; // declaration statement
  cout << n; // expression statement
} // end of block, end of if-statement

Each compound statement introduces its own block scope: variables declared inside a block are destroyed at the closing brace in reverse order.

int main()
{
    { // start of block
       std::ofstream f("test.txt"); // declaration statment
       f << "hi\n"; // expression statement
    } // end of block, f is flushed and closed by ofstream's destructor
    std::ifstream f("test.txt"); 
    std::string str;
    f >> str; 
}

Selection statement

A selection statement chooses between one of several flows of control.

attr(optional) if ( condition ) statement	(1)
attr(optional) if ( condition ) statement else statement	(2)
attr(optional) switch ( condition ) statement	(3)

1) if statement

2) if statement with an else clause

3) switch statement

Iteration statement

An iteration statement repeatedly executes some code.

attr(optional) while ( condition ) statement	(1)
attr(optional) do statement while ( expression ) ;	(2)
attr(optional) for ( for-init-statement condition(optional) ; expression(optional) ) statement	(3)
attr(optional) for ( for-range-decl : for-range-init ) statement	(4)	(since C++11)

1) while loop

2) do-while loop

3) for loop

4) range for loop

Jump statement

A jump statement unconditionally transfers flow control.

attr(optional) break ;	(1)
attr(optional) continue ;	(2)
attr(optional) return expression(optional) ;	(3)
attr(optional) return braced-init-list ;	(4)	(since C++11)
attr(optional) goto identifier ;	(5)

1) break statement

2) continue statement

3) return statement with an optional expression

4) return statement using list initialization

5) goto statement

Note: for all jump statements, transfer out of a loop, out of a block, or back past an initialized variable with automatic storage duration involves the destruction of objects with automatic storage duration that are in scope at the point transferred from but not at the point transferred to. If multiple objects were initialized, the order of destruction is the opposite of the order of initialization.

Declaration statement

A declaration statement introduces one or more identifiers into a block.

block-declaration ;	(1)

1) See Declarations and Initialization for details.

Try block statement

A try block statement provides the ability to catch exceptions thrown when executing other statements.

attr(optional) try compound-statement handler-sequence	(1)

1) See try/catch for details.

See also

C documentation for Statements