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programming puzzles

作者：吴永铮 (等级：8 - 融会贯通，发帖：2078) 发表：2007-04-24 17:12:48　楼主　关注此帖评分：

programming puzzles

Write a "Hello World" program in 'C' without using a semicolon.
(this is tricky)

C/C++ : Exchange two numbers without using a temporary variable.
(somehow classic way)

C/C++ : Find if the given number is a power of 2.
(somehow classic way)

Write a program whose printed output is an exact copy of the source. Needless to say, merely echoing the actual source file is not allowed.
(a bit hard to think)

source: http://developers.slashdot.org/article.pl?sid=04/12/04/0116231

Put your OWN COOL signature here!

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作者：吴永铮 (等级：8 - 融会贯通，发帖：2078) 发表：2007-04-25 12:26:14　 2楼

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在 icky 的大作中提到：

what do you mean by classic way?C/C++ : Find if the given number is a power of 2. (somehow classic way) can i check bit by bit?

(3) can be done by less than 5 instructions

By classic (or classical?), I mean a lot of people use the method.

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作者：吴永铮 (等级：8 - 融会贯通，发帖：2078) 发表：2007-04-25 15:26:25　 3楼

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在 icky 的大作中提到：

check equality with all 2's powerthere are at most 32 of them...

can be simpler and faster

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作者：吴永铮 (等级：8 - 融会贯通，发帖：2078) 发表：2007-04-26 00:50:18　 4楼

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在这就是生活的大作中提到：

(num > 0) && (((num - 1) & num) == 0) ?

correct

just ((num - 1) & num) is enough

((num - 1) ^ num) also can

It's quite practical and quite frequent. It's important to know it, otherwise you don't understand what's going on.

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作者：吴永铮 (等级：8 - 融会贯通，发帖：2078) 发表：2007-04-26 01:06:43　 5楼

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在吴永铮的大作中提到：

correctjust ((num - 1) & num) is enough ((num - 1) ^ num) also can It's quite practical and quite frequent. It's important to know it, otherwise you don't understand what's going on.

opps ^ is wrong. It's always true.

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作者：吴永铮 (等级：8 - 融会贯通，发帖：2078) 发表：2007-04-27 21:56:17　 6楼评分：

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在吴永铮的大作中提到：

programming puzzlesWrite a "Hello World" program in 'C' without using a semicolon. (this is tricky) C/C++ : Exchange two numbers without using a temporary variable. (somehow classic way) C/C++ : Find if the given number is a power of 2. (somehow classic way) Write a program whose printed output is an exact copy of the source. Needless to say, merely echoing the actual source file is not allowed. (a bit hard to think) source: http://developers.slashdot.org/article.pl?sid=04/12/04/0116231

my answer to (4)

#include <stdio.h>
int main (void)
{
const char *str = "#include <stdio.h>%cint main (void)%c{%c const char *str = %c%s%c;%c printf(str, 10, 10, 10, 34, str, 34, 10, 10, 10, 10);%c return 0;%c}%c";
printf(str, 10, 10, 10, 34, str, 34, 10, 10, 10, 10);
return 0;
}

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