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 |
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) |
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):
int j = 1; if (i > 1) if(j > 2) printf("%d > 1 and %d > 2\n", i, j); else // this else is part of if(j>2), not part of if(i>1) printf("%d > 1 and %d <= 2\n", i, j);
If statement-true is entered through a goto, statement-false is not executed.
Run this code
#include <stdio.h> int main(void) { int i = 2; if (i > 2) { printf("first is true\n");