help with lists

This is a discussion on help with lists within the C Programming forums, part of the General Programming Boards category; Below is a program ive written to test if a number entered is a perfect number. However im having problems ...

  1. #1
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    Question help with lists

    Below is a program ive written to test if a number entered is a perfect number. However im having problems with making another function that will lists the perfect numbers from 1 to 1000. Any help or hints will be appreciated. Thanks

    Code:
    #include <stdio.h>
    
    int factors( int );
    int perfect( int );
    
    int main()
    {
    	int number;
    
    	printf("Enter Number: " );
    	scanf( "%d", &number );
    
    	printf( "%d\n", perfect( number ) );
    
    	return 0;
    }
    
    int factors( number )
    {
    	int counter = 1, counter2 = 0, newNumber;
    
    	while ( counter <= number ) {
    		if ( ( number % counter == 0 ) && ( number != counter ) ) {
    			newNumber = counter;
    			counter2 += newNumber;
    		}
    		counter++;
    	}
    
    	return counter2;
    }
    
    
    int perfect( number )
    {
    	if ( number == factors( number ))
    		return 1;
    	else
    		return 0;
    }
    there are only 10 people in the world, those who know binary and those who dont

  2. #2
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    Well you're going to have to use a loop. It will probably look something like this:

    Code:
    /* Headers and forward declarations */
    #define MAX_NUM 1000
    
    int main()
    {
      int i;
    
      for( i = 0; i < MAX_NUM; ++i )
      {
        if( perfect( i ) )
        {
          printf( "%d\n", i );
        }
      }
    
      return 0;
    }
    I think something like that will probably do it. I think you should be able to tell what is going on in the loop as it is fairly straight-forward. If you need help understanding it let me know. Basically we will execute the commands within the for loop braces until the middle condition ( i < MAX_NUM ) is false.
    Last edited by MrWizard; 01-28-2003 at 02:55 AM.
    "...the results are undefined, and we all know what "undefined" means: it means it works during development, it works during testing, and it blows up in your most important customers' faces." --Scott Meyers

  3. #3
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    Ive implemented what you have said and understand what is going on but i think im still missing something, you have declared int number, but it's not doing anything..
    there are only 10 people in the world, those who know binary and those who dont

  4. #4
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    Originally posted by kurz7
    Ive implemented what you have said and understand what is going on but i think im still missing something, you have declared int number, but it's not doing anything..
    Yeah you're right, I just copied and pasted your code for a starting point. You used number but I didn't. Take it out, you'll be fine. It should still work fine?

  5. #5
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    hmm not sure why its not working.
    Just thinking about the code, will the counter always restart to 0 when the new number is called? Might keep incrementing so it will probably do 1 % 1, then 2 % 2 ...

    i cuold be wrong
    there are only 10 people in the world, those who know binary and those who dont

  6. #6
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    I didn't look at your perfect number algorithm at all. I was just showing you how to setup a for loop and use it. The loop index i should not be the problem. If you can't fix it by tomorrow let me know.

  7. #7
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    ive fixed the code to generate perfect numbers from 1 to 1000 but it still doesnt seem to be working.. not sure what the problem is, could be the counters.

    Code:
    #include <stdio.h>
    #define MAX_NUM 1000
    
    int factors( int );
    int perfect( int );
    
    int main()
    {
      int i;
    
      for( i = 0; i < MAX_NUM; ++i )
      {
        if( perfect( i ) )
        {
          printf( "%d\n", i );
        }
      }
    
      return 0;
    }
    
    int factors( number )
    {
            int counter = 1, counter2 = 0, newNumber;
    
            while ( counter <= number ) {
                    if ( ( number % counter == 0 ) && ( number != counter ) ) {
                            newNumber = counter;
                            counter2 += newNumber;
                    }
                    counter++;
            }
    
            return counter2;
    }
    
    
    int perfect( number )
    {
            if ( number == factors( number ))
                    return 1;
            else
                    return 0;
    }
    there are only 10 people in the world, those who know binary and those who dont

  8. #8
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    Program works fine for me. Start the loop counter at 1 instead of 0 because it reports 0 as a perfect number when in fact it is not. Again, program works for me.

  9. #9
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    hmm still doesnt seem to work, there should be 3 perfect numbers between 1 and 1000, did u get all 3? 6, 28, and another one ive forgotten..

    it doesnt output anything
    there are only 10 people in the world, those who know binary and those who dont

  10. #10
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    Output:
    0
    6
    28
    496
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  11. #11
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    still doesnt work
    is it a compiler problem? im on mandrake 8.2 and just using the gcc commands.
    there are only 10 people in the world, those who know binary and those who dont

  12. #12
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    Originally posted by kurz7
    still doesnt work
    is it a compiler problem? im on mandrake 8.2 and just using the gcc commands.
    Put some extra printf() statements in there to help you debug it. Also, try fflush(stdout); at the end of the program (shouldn't be necessary but you never know )
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

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