if statement
From cppreference.com
Conditionally executes code.
Used where code needs to be executed only if some condition is true.
Syntax
attr-spec-seq(optional) if ( expression ) statement-true
|
(1) | ||||||||
attr-spec-seq(optional) if ( expression ) statement-true else statement-false
|
(2) | ||||||||
attr-spec-seq | - | (C23)optional list of attributes, applied to the if statement
|
expression | - | an expression of any scalar type |
statement-true | - | any statement (often a compound statement), which is executed if expression compares not equal to 0 |
statement-false | - | any statement (often a compound statement), which is executed if expression compares equal to 0 |
Explanation
expression must be an expression of any scalar type.
If expression compares not equal to the integer zero, statement-true is executed.
In the form (2), if expression compares equal to the integer zero, statement_false is executed.
As with all other selection and iteration statements, the entire if-statement has its own block scope: enum {a, b}; int different(void) { if (sizeof(enum {b, a}) != sizeof(int)) return a; // a == 1 return b; // b == 0 in C89, b == 1 in C99 } |
(since C99) |
Notes
The else
is always associated with the closest preceding if
(in other words, if statement-true is also an if statement, then that inner if statement must contain an else
part as well):
If statement-true is entered through a goto, statement-false is not executed.
Keywords
Example
Run this code
Output:
first is false i == 3 i != 3 is false
References
- C17 standard (ISO/IEC 9899:2018):
- 6.8.4.1 The if statement (p: 108-109)
- C11 standard (ISO/IEC 9899:2011):
- 6.8.4.1 The if statement (p: 148-149)
- C99 standard (ISO/IEC 9899:1999):
- 6.8.4.1 The if statement (p: 133-134)
- C89/C90 standard (ISO/IEC 9899:1990):
- 3.6.4.1 The if statement