Perfect Number

 #include <stdio.h>

int main()
{
 //The first perfect number is 6, because 1, 2, and 3
 //are its proper positive divisors, and 1 + 2 + 3 = 6.

 int n, i = 1, sum = 0;

 printf("Enter a number: ");
 scanf("%d", &n);

 while (i < n)
 {
  if (n % i == 0)
  {
   sum = sum + i;
  }
  i++;
 }

 if (sum == n)
 {
  printf("%d is a perfect number", i);
 }
 else
 {
  printf("%d is not a perfect number", i);
 }
  
 return 0;
}

OUTPUT

Enter a number: 6
6 is a perfect number