1. Definition

	A perfect number is a positive integer equal to the sum of 
	its proper positive divisors (excluding itself); or the half of the sum 
	of all of its positive divisors (including itself).
	Example:
	--------
	Propres divisors of 6: 1,2,3. Their somme = 1+2+3 = 6.
	Divisors of 6: 1,2,3,6. Their half somme = (1+2+3+6)/2 = 6.

	2. Example in C language:
	

	#include <stdio.h>
	#include <math.h>
	enum BOOLEAN { false, true };

	//Test is it perfect ?
	int perfect(int number)
	{
	int n;
	int sum =0;

	for ( n = 1 ; n <= number-1 ; n++ )
	{
		if ( number% n == 0 )
		{
		sum += n;
		}
	}

	if (sum == number)
	{
	return true;
	}
	else
	{
	return false;
	}
	}

	//Displying ..
	
	int display_perfect(int number)
	{
	int m = number;
		if (perfect(m))
		{
		printf("\n The number %d is perfect. \n", number);
		}
		else
		{
		printf("\n The number %d is not perfect. \n", number);
		}

	return 0;
	}


	int main()
	{
	int number;
	printf("\n Enter an integer ?: --> ");
	scanf("%d", &number);
	int m = number;
	display_perfect(m);

	//Perfect positive integers betwenn two values ..
	
	int a,b;
	int count=0;//To count them:
	printf("\n Enter two integer limits : --> \n");
	scanf(" %d %d", &a,&b);

	printf("\n The perfect numbers between %d and %d are: \n",a,b);
	int n;
	for ( n = a ; n <= b ; n++ )
	{
		if ( perfect(n) )
		{
		count += 1;
		printf("\n %d) %d \n",count,n);
		}

	}
		if (count ==0)
		{
		printf("\n No perfect number between %d and %d \n", a,b);
		}

	printf("\n");
	return 0;
	}