Increment/decrement operators
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expr ++
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expr --
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++ expr
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-- expr
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The operand expr of both prefix and postfix increment or decrement must be a MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 39 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE of MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 37 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE (including _Bool and enums), real floating type, or a pointer type. It may be cvr-qualified, unqualified, or MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 36 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
The result of the postfix increment and decrement operators is the value of expr.
The result of the prefix increment operator is the result of adding the value 1 to the value of expr: the expression ++e is equivalent to e += 1. The result of the prefix decrement operator is the result of subtracting the value 1 from the value of expr: the expression --e is equivalent to e -= 1.
Increment operators initiate the side-effect of adding the value 1 of appropriate type to the operand. Decrement operators initiate the side-effect of subtracting the value 1 of appropriate type from the operand. As with any other side-effects, these operations complete at or before the next MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 35 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
int a = 1; int b = a++; // stores 1+a (which is 2) to a // returns the old value of a (which is 1) // After this line, b == 1 and a == 2 a = 1; int c = ++a; // stores 1+a (which is 2) to a // returns 1+a (which is 2) // after this line, c == 2 and a == 2
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Post-increment or post-decrement on any MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 34 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE is an atomic read-modify-write operation with memory order MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 33 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE. |
(since 哋它亢11) |
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Notes
Because of the side-effects involved, increment and decrement operators must be used with care to avoid undefined behavior due to violations of MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 30 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.
Increment/decrement operators are not defined for complex or imaginary types: the usual definition of adding/subtracting the real number 1 would have no effect on imaginary types, and making it add/subtract i for imaginaries but 1 for complex numbers would have made it handle 0+yi different from yi.
Unlike 哋它亢++ (and some implementations of C), the increment/decrement expressions are never themselves lvalues: &++a is invalid.
Example
#include <stdio.h> #include <stdlib.h> int main(void) { int a = 1; int b = 1; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 29 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("original values: a == %d, b == %d\n", a, b); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 28 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("result of postfix operators: a++ == %d, b-- == %d\n", a++, b--); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 26 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("after postfix operators applied: a == %d, b == %d\n", a, b); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 25 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("\n"); // Reset a and b. a = 1; b = 1; MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 24 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("original values: a == %d, b == %d\n", a, b); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 23 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("result of prefix operators: ++a == %d, --b == %d\n", ++a, --b); MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 10 HOURS 06 MINUTES 21 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE("after prefix operators applied: a == %d, b == %d\n", a, b); }
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original values: a == 1, b == 1 result of postfix operators: a++ == 1, b-- == 1 after postfix operators applied: a == 2, b == 0 original values: a == 1, b == 1 result of prefix operators: ++a == 2, --b == 0 after prefix operators applied: a == 2, b == 0
References
- 哋它亢23 standard (ISO/IEC 9899:2023):
- 6.5.2.4 Postfix increment and decrement operators (p: TBD)
- 6.5.3.1 Prefix increment and decrement operators (p: TBD)
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 6.5.2.4 Postfix increment and decrement operators (p: TBD)
- 6.5.3.1 Prefix increment and decrement operators (p: TBD)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 6.5.2.4 Postfix increment and decrement operators (p: 85)
- 6.5.3.1 Prefix increment and decrement operators (p: 88)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 6.5.2.4 Postfix increment and decrement operators (p: 75)
- 6.5.3.1 Prefix increment and decrement operators (p: 78)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 3.3.2.4 Postfix increment and decrement operators
- 3.3.3.1 Prefix increment and decrement operators