将复合语句放在for循环的条件中 [英] Putting a composite statement in the condition of a for loop
问题描述
以下是一个问题遇到相当频繁:
打印一系列数字;在它们之间打印一个空格,最后输入一个回车符(但是没有空格)。 b
$ b
显而易见的解决方案是使最后一个(或第一个)语句成为一个特例。我正在思考如何使这个更高效/紧凑。
$ b $对于(ii = 0; ii <4; ii ++)而言,强力: {
printf(%d,ii);
if(ii <3)printf(); else printf(\\\
);
}
请注意,这涉及一个条件的两个评估。
展开:
for(ii = 0; ii <3; ii ++){
printf(%d,ii):
}
printf(%d\\\
,ii);
利用事实上,当我们离开循环时, ii
将会最后一次递增。
功能我想
ii = 0;
while(1){
printf(%d,ii);
ii ++;
if(ii <3)printf();
else {printf(\\\
); break;}
}
我想知道是否可以在用于
语句。我修了一下,发现下面的工作(有点令我惊讶......它确实需要括号,而且它在?:
和,
operators - 参见 http://codepad.org/wFa2YwCg ) :(ii)(ii)(ii <3)?(printf(%d,ii),1):
pre $ :(输出( %d\\\
,ⅱ),0);ⅱ++);
我基本上将评估这个条件
for循环的一部分变成了一个在大部分循环中执行这个语句,而这另一个用于最后一个循环
语句。
我想知道是否有更好的方法来做到这一点 - 既有效率又可读?
许多方式应该关闭这个问题,因为它是基于意见的。]
这个问题经常出现。我总是选择一个解决方案来最小化迭代部分的指令。
{/ *不要污染外部范围ii * /
int ii; (ii = 0; ii <3; ++ ii / *)的
,我总是喜欢这个到ii ++ * /){
printf(%d,ii);
}
printf(%d \\\
,ii);
$ / code>
三元, if
声明等只是混淆的东西。在我看来。
I have a contrived example to demonstrate the request for a specific functionality - I wonder if anyone has a clever trick to do this.
The following is a problem one encounters quite frequently:
"Print a series of numbers; print a space between them, and a carriage return (but no space) at the end.
The obvious solution is to make the last (or first) statement a special case. I was pondering ways to make this more efficient/compact.
brute force:
for(ii=0; ii<4; ii++) {
printf("%d", ii);
if(ii<3) printf(" "); else printf("\n");
}
Note that this involves two evaluations of a condition.
unrolling:
for(ii=0; ii<3; ii++) {
printf("%d ", ii):
}
printf("%d\n", ii);
Leverages the fact that ii
will be incremented one last time as we leave the loop.
functionality I would like
ii = 0;
while(1) {
printf("%d", ii);
ii++;
if(ii<3) printf(" ");
else {printf("\n"); break;}
}
And I was wondering if it's possible to make this work inside the for
statement. I tinkered a bit, and found that the following works (somewhat to my surprise... it did need the parentheses, and it quite unreadable between the ?:
and the ,
operators - see http://codepad.org/wFa2YwCg):
for(ii=0; (ii<3)?(printf("%d ",ii),1):(printf("%d\n",ii),0);ii++);
I am essentially turning the evaluate this condition
part of the for loop into a execute this statement for most of the loop, and this other one for the last pass
statement.
I was wondering if there is a better way to do this - both efficient, and readable?
[In many ways this question should be closed as it's opinion based.]
This problem crops up often. I always opt for a solution that minimises the instructions in the iterative part.
{ /*don't pollute the outer scope with ii*/
int ii;
for (ii = 0; ii < 3; ++ii/*I've always preferred this to ii++*/) {
printf("%d ", ii);
}
printf("%d\n", ii);
}
Ternaries, if
statements etc. just obfuscate things. In my opinion.
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