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Statements

Statements are fragments of the C program that are executed in sequence. The body of any function is a compound statement, which, in turn is a sequence of statements and declarations:

-
int main(void)
-{ // start of a compound statement
-    int n = 1; // declaration (not a statement)
-    n = n+1; // expression statement
-    printf("n = %d\n", n); // expression statement
-    return 0; // return statement
-} // end of compound statement, end of function body


There are five types of statements:

-
-1) compound statements -
-2) expression statements -
-3) selection statements -
-4) iteration statements -
-5) jump statements -
- -

An attribute specifier sequence (attr-spec-seq) can be applied to an unlabeled statement, in which case (except for an expression statement) the attributes are applied to the respective statement.

-		 (since C23)

Labels

Any statement can be labeled, by providing a name followed by a colon before the statement itself.

- - - - -
attr-spec-seq(optional)(since C23) identifier : (1)
attr-spec-seq(optional)(since C23) case constant-expression : (2)
attr-spec-seq(optional)(since C23) default : (3)
-1) Target for goto.
-2) Case label in a switch statement.
-3) Default label in a switch statement.

Any statement (but not a declaration) may be preceded by any number of labels, each of which declares identifier to be a label name, which must be unique within the enclosing function (in other words, label names have function scope).

-

Label declaration has no effect on its own, does not alter the flow of control, or modify the behavior of the statement that follows in any way.

- - - - -

A label shall be followed by a statement.

-		 (until C23)

A label can appear without its following statement. If a label appears alone in a block, it behaves as if it is followed by a null statement.

-

The optional attr-spec-seq is applied to the label.

-		 (since C23)

Compound statements

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

- - - -
{ statement | declaration...(optional) } (until C23)
attr-spec-seq(optional) { unlabeled-statement | label | declaration...(optional) } (since C23)

The compound statement allows a set of declarations and statements to be grouped into one unit that can be used anywhere a single statement is expected (for example, in an if statement or an iteration statement):

-
if (expr) // start of if-statement
-{ // start of block
-  int n = 1; // declaration
-  printf("%d\n", n); // expression statement
-} // end of block, end of if-statement

Each compound statement introduces its own block scope.

-

The initializers of the variables with automatic storage duration declared inside a block and the VLA declarators are executed when flow of control passes over these declarations in order, as if they were statements:

-
int main(void)
-{ // start of block
-  { // start of block
-       puts("hello"); // expression statement
-       int n = printf("abc\n"); // declaration, prints "abc", stores 4 in n
-       int a[n*printf("1\n")]; // declaration, prints "1", allocates 8*sizeof(int)
-       printf("%zu\n", sizeof(a)); // expression statement
-  } // end of block, scope of n and a ends
-  int n = 7; // n can be reused
-}

Expression statements

An expression followed by a semicolon is a statement.

- - - -
expression(optional) ; (1)
attr-spec-seq expression ; (2) (since C23)

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 or before a declaration:

-
puts("hello"); // expression statement
-char *s;
-while (*s++ != '\0')
-    ; // null statement
- -

The optional attr-spec-seq is applied to the expression.

-

An attr-spec-seq followed by ; does not form an expression statement. It forms an attribute declaration instead.

-		 (since C23)

Selection statements

The selection statements choose between one of several statements depending on the value of an expression.

- - - - -
attr-spec-seq(optional)(since C23) if ( expression ) statement (1)
attr-spec-seq(optional)(since C23) if ( expression ) statement else statement (2)
attr-spec-seq(optional)(since C23) switch ( expression ) statement (3)
-1) if statement
-2) if statement with an else clause
-3) switch statement

Iteration statements

The iteration statements repeatedly execute a statement.

- - - - -
attr-spec-seq(optional)(since C23) while ( expression ) statement (1)
attr-spec-seq(optional)(since C23) do statement while ( expression ) ; (2)
attr-spec-seq(optional)(since C23) for ( init-clause ; expression(optional) ; expression(optional) ) statement (3)
-1) while loop
-2) do-while loop
-3) for loop

Jump statements

The jump statements unconditionally transfer flow control.

- - - - - -
attr-spec-seq(optional)(since C23) break ; (1)
attr-spec-seq(optional)(since C23) continue ; (2)
attr-spec-seq(optional)(since C23) return expression(optional) ; (3)
attr-spec-seq(optional)(since C23) goto identifier ; (4)
-1) break statement
-2) continue statement
-3) return statement with an optional expression
-4) goto statement

References

See also

-
C++ documentation for Statements
-

- © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
- https://en.cppreference.com/w/c/language/statements -

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