How to write a program for...

This is a discussion on How to write a program for... within the C Programming forums, part of the General Programming Boards category; I need to write a program to print all combinations of 1, 2 and 3 using for loop. Now I ...

  1. #1
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    How to write a program for...

    I need to write a program to print all combinations of 1, 2 and 3 using for loop.

    Now I am just able to think of a logic as to how to do it.

    Can somebody guide me please.

    Thanks in advance

    Cheers
    babyboy

  2. #2
    C++ Witch laserlight's Avatar
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    Now I am just able to think of a logic as to how to do it.
    What is the solution you have in mind?
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    I can print all 3 numbers in reverse or forward using a for loop. But after that I am just not sure what to do.

    I know that i will have to use a nested for loop, but dont know exactly how.

  4. #4
    C++まいる!Cをこわせ!
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    But you aren't exactly telling your whole solution to the problem.
    If you pointed out how, exactly, in steps how you would do it?
    It should be easy to understand how to make the code once you fully understand how you would do it in real life.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    To be honest even I have not thought of it like that... as in terms of steps. please give me 5 mins and let me try :-)

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    I am not able to come up with anything. I am sitting here looking at the screen and my mind is blank.

    Can you please give me a step by step break up and let me try coding it please.

  7. #7
    C++まいる!Cをこわせ!
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    I'm telling you that you should have a logic on how you want to do it first.
    So say you got a paper, how would you write down all those possible combinations?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  8. #8
    Algorithm Dissector iMalc's Avatar
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    Lets start by looking at the expected output:
    (), (1), (2), (3), (1,2), (1,3), (2,3), (1,2,3)
    Of course the order you output these probably doesn't matter, so long as each one is only printed once.
    Now I'll happily state for you that to list all the combinations than include the numbers from 1 to n, you can first generate all the combinations from 1 to n-1, and then duplicate them, adding n to each element in the copy.
    e.g. Here are the combinations of 1 and 2: (), (1), (2), (1,2).
    And here are the combinations of 1: (), (1). See the pattern?
    Applying that rule recursively gives you one possible answer, though it can also easily enough be done without recursion.
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    I was assuming the OP was looking for permutations, like this:

    1 2 3
    1 3 2
    2 1 3
    2 3 1
    3 1 2
    3 2 1

    If this assumption is correct, your simplest solution will involve 3 nested for loops each going from 1 to 3. Code that up, including a printf, and look at the ouput. Then use an if statement to filter out the ones you don't want. What do they have in common?

    I also assume that "babyboy" is a girl. What guy would call themselves babyboy?
    (Then again, what woman would put a bragging quote in their signature?)

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    using recursion:
    Code:
    void Show(int arr[], size_t n)
    {
    for(int i=0;i<n;i++)     
     if(arr[i]!=0)
       printf("%d,",arr[i]); 
    putchar(10);
    }
    
    void Combination(int k, int arr[], size_t n)
    {
     if(k>=n) return;
     
     Combination(k+1,arr, n);  
     arr[k]+=(k+1);
     Show(arr, n); 
     Combination(k+1,arr, n);  
     arr[k]-=(k+1);
    }
    
    int main()
    {   
    int arr[3]={0};    
    Combination(0, arr, 3);   
    getchar();  
    return 0;
    }
    Which will work for any number combinations.
    Last edited by 52Cent; 02-17-2008 at 07:04 PM.

  11. #11
    C++まいる!Cをこわせ!
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    Don't give solutions to people.
    And try indenting that code a little better, as well.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  12. #12
    CSharpener vart's Avatar
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    Also do not use magic constants
    putchar(10);

    It should be

    putchar('\n');
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    the last 10% takes the other 90% of the time.

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    Quote Originally Posted by oogabooga View Post
    I was assuming the OP was looking for permutations, like this:

    1 2 3
    1 3 2
    2 1 3
    2 3 1
    3 1 2
    3 2 1

    If this assumption is correct, your simplest solution will involve 3 nested for loops each going from 1 to 3. Code that up, including a printf, and look at the ouput. Then use an if statement to filter out the ones you don't want. What do they have in common?

    I also assume that "babyboy" is a girl. What guy would call themselves babyboy?
    (Then again, what woman would put a bragging quote in their signature?)

    also shouldnt i be printing
    111
    222
    333

    And does it really matter if i am boy or a gal

  14. #14
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by oogabooga View Post
    I was assuming the OP was looking for permutations
    Why would you assume that? There had been nothing posted so far that suggested what was asked for wasn't what was desired.
    If someone know's the difference, they know which to ask for, if they don't they usually just copy what the assignment says.

    111, 222, and 333 are neither combinations of 1, 2, and 3, nor permutations.
    If you want to know the difference, then the answer is easily found:
    http://www.google.com/search?hl=en&q...utations&meta=
    If you are sure that 111 etc should be part of your output then you're wanting for something totally unrelated to what you asked for.
    I think perhaps you should state what YOU want the output to be, so we are all on the same page.
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  15. #15
    C++ Witch laserlight's Avatar
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    111, 222, and 333 are neither combinations of 1, 2, and 3, nor permutations.
    They are valid permutations if repetition is allowed.
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