So, that's the question: can I increment the i variable inside for loop?:
for(int i = 0; i < 1000; i++)
{
i++; // is this legal? if not what is the alternative?
}
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6It's perfectly legal. Have you tried it?Baldrick– Baldrick2014-01-13 02:19:52 +00:00Commented Jan 13, 2014 at 2:19
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yes, it somehow doesn't work, maybe i'm doing something wrong... But the purpose of the question was to ask if it is a good practice to do so, if it's possible.Dima Knivets– Dima Knivets2014-01-13 02:20:48 +00:00Commented Jan 13, 2014 at 2:20
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4What doesn't work? Maybe update your question with what seems to be unexpected about the resulting behaviour.Baldrick– Baldrick2014-01-13 02:21:22 +00:00Commented Jan 13, 2014 at 2:21
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It's legal, but it is meant exceptional processing probably.BLUEPIXY– BLUEPIXY2014-01-13 02:22:38 +00:00Commented Jan 13, 2014 at 2:22
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OK, thanks, I'll try to debug a bit more time, if I don't manage to get it working I'll post the broken code.Dima Knivets– Dima Knivets2014-01-13 02:25:53 +00:00Commented Jan 13, 2014 at 2:25
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2 Answers
Absolutely legal but not very intuitive.
Consider using a while loop instead if you need to manipulate your looping in this way (it's just a code clarity thing, not a legal thing).
Comments
If we look at the C99 draft standard it says the following about the for loop in section 6.8.5.3 The for statement:
The statement
for ( clause-1 ; expression-2 ; expression-3 ) statement
behaves as follows: The expression expression-2 is the controlling expression that is evaluated before each execution of the loop body. The expression expression-3 is evaluated as a void expression after each execution of the loop body. If clause-1 is a declaration, the scope of any identifiers it declares is the remainder of the declaration and the entire loop, including the other two expressions; it is reached in the order of execution before the first evaluation of the controlling expression. If clause-1 is an expression, it is evaluated as a void expression before the first evaluation of the controlling expression.137)
So if we parse this text your for loop will be roughly equivalent to the following:
{
int i = 0 ; // clause 1
while( i < 1000 ) //expression 2
{
i++ ; // statement
i++ ; // expression 3
}
}
which is valid code but you would probably not write the code this way if you translated it out by hand.
Comments
