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:
intmain(void){// start of a compound statementintn=1;// declaration (not a statement)n=n+1;// expression statementprintf("n = %d\n",n);// expression statementreturn0;// return statement}// end of compound statement, end of function body
There are five types of statements:
An
(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)caseconstant-expression:(2) attr-spec-seq(optional)(since C23)default:(3) 1) Target for
.
2) Case label in a
statement.
3) Default label in a
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
).
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
.
The optional
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
statement or an iteration statement):
if(expr)// start of if-statement{// start of blockintn=1;// declarationprintf("%d\n",n);// expression statement}// end of block, end of if-statementEach compound statement introduces its own
.
The initializers of the variables with automatic
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:
intmain(void){// start of block{// start of blockputs("hello");// expression statementintn=printf("abc\n");// declaration, prints "abc", stores 4 in ninta[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 endsintn=7;// n can be reused}Expression statements
An expression followed by a semicolon is a statement.
expression(optional);(1) attr-spec-seqexpression;(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
or
loop. It can also be used to carry a label in the end of a compound statement or before a declaration:
puts("hello");// expression statementchar*s;while(*s++!='\0');// null statementThe optional
is applied to the expression.
An attr-spec-seq followed by ; does not form an expression statement. It forms an
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)statementelsestatement(2) attr-spec-seq(optional)(since C23)switch(expression)statement(3) 1)
statement
2)
statement with an else clause
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)dostatementwhile(expression);(2) attr-spec-seq(optional)(since C23)for(init-clause;expression(optional);expression(optional))statement(3) 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)returnexpression(optional);(3) attr-spec-seq(optional)(since C23)gotoidentifier;(4) 3)
statement with an optional expression
4)
statement
References
C23 standard (ISO/IEC 9899:2024):
6.8 Statements and blocks (p: TBD)
C17 standard (ISO/IEC 9899:2018):
6.8 Statements and blocks (p: 106-112)
C11 standard (ISO/IEC 9899:2011):
6.8 Statements and blocks (p: 146-154)
C99 standard (ISO/IEC 9899:1999):
6.8 Statements and blocks (p: 131-139)
C89/C90 standard (ISO/IEC 9899:1990):
3.6 STATEMENTS
See also