Guess the code!

This is a discussion on Guess the code! within the C++ Programming forums, part of the General Programming Boards category; An easy one: Code: int a[] = {11,12,13,14,15}; int* ap = a - 1;...

  1. #76
    (?<!re)tired Mario F.'s Avatar
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    An easy one:

    Code:
    int a[] = {11,12,13,14,15};
    int* ap = a - 1;
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  2. #77
    Just Lurking Dave_Sinkula's Avatar
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    That's just evil.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #78
    (?<!re)tired Mario F.'s Avatar
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    And yet that's correct
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  4. #79
    Cat without Hat CornedBee's Avatar
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    Are you absolutely sure? The standard is far more precise about what operations are allowed on pointers and when than what any implementation actually enforces.

    Hmm, according to the C faq link it's not correct.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  5. #80
    (?<!re)tired Mario F.'s Avatar
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    I meant Dave was correct on how he interpreted the code. It's a way to implement a unit-based array.

    EDIT: I was actually unware at the fact that despite there existing no dereferencing it could still produce undefined behavior. But Dave hit it on the nail at the code usage.
    Last edited by Mario F.; 11-11-2006 at 12:01 PM.
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  6. #81
    Algorithm engineer
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    Quote Originally Posted by Mario F.
    An easy one:

    Code:
    int a[] = {11,12,13,14,15};
    int* ap = a - 1;
    But is there actually systems that behaves differenty than expected, trying to "wrap around" for example?

  7. #82
    (?<!re)tired Mario F.'s Avatar
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    > But is there actually systems that behaves differenty than expected, trying to "wrap around" for example?

    Some people don't like to admit they were wrong, apparently.

    While the link provided by Dave explains why it is undefined behavior, the following link from the Numerical Recipes book website shows an extract of the new Numerical Recipes for C++ book. Take a look at page 10. It's worth your time... although probably make you mad.

    http://www.numerical-recipes.com/cpppages/chap1sel.pdf
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  8. #83
    Just Lurking Dave_Sinkula's Avatar
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    For fun:
    Code:
    void foo(unsigned int value)
    {
       unsigned int bit;
       for ( bit = /* msb */(~0U >> 1) + 1; bit > 0; bit >>= 1 )
       {
          putchar("01"[!!(value & bit)]);
       }
       putchar('\n');
    }
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  9. #84
    Cat without Hat CornedBee's Avatar
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    Ain't that just a base 2 itoa, printing directly?
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  10. #85
    Algorithm engineer
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    Mario F: I think you missunderstod me, I was just being curious.
    Last edited by TriKri; 11-11-2006 at 05:33 PM.

  11. #86
    (?<!re)tired Mario F.'s Avatar
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    Quote Originally Posted by TriKri
    Mario F: I think you missunderstod me, I was just being curious.
    Oh. I have. Sorry. I read that as a rethorical question.
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  12. #87
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by CornedBee
    Ain't that just a base 2 itoa, printing directly?
    Yeah. I was kind of shooting for something along the line of, "the !!(value & bit) results in a one or a zero if the selected bit is set in value or not, so you can safely index into the string literal", or something.
    Code:
    putchar("01"[!!(value & bit)]);
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  13. #88
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    Quote Originally Posted by Dave_Sinkula
    Yeah. I was kind of shooting for something along the line of, "the !!(value & bit) results in a one or a zero if the selected bit is set in value or not, so you can safely index into the string literal" [/code]
    what if you'd do (value & bit) != 0 ? isnt that either 0 or 1 ?

  14. #89
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    But!! isn't!! double!! exclaimation!! so!! leet!! ??!!
    Code:
    #include <stdio.h>
    
    void J(char*a){int f,i=0,c='1';for(;a[i]!='0';++i)if(i==81){
    puts(a);return;}for(;c<='9';++c){for(f=0;f<9;++f)if(a[i-i%27+i%9
    /3*3+f/3*9+f%3]==c||a[i%9+f*9]==c||a[i-i%9+f]==c)goto e;a[i]=c;J(a);a[i]
    ='0';e:;}}int main(int c,char**v){int t=0;if(c>1){for(;v[1][
    t];++t);if(t==81){J(v[1]);return 0;}}puts("sudoku [0-9]{81}");return 1;}

  15. #90
    MFC killed my cat! manutd's Avatar
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    Ah! Not the leet thing again!
    Silence is better than unmeaning words.
    - Pythagoras
    My blog

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