perfect_number.cpp

/*
A program to check whether the given number is a perfect number or not.

Perfect number is a positive whole number that is equal to the sum of its proper divisors.

The first perfect number is 6 as the sum of its proper positive divisors, 1,2 and 3 is 6.
Other perfect numbers are 28, 496, 8128,etc.
*/

#include<iostream>
using namespace std;


//function to check perfect number
void check_perfect_number(int num)
{

    int sum = 0;
    int i;


    //loop till half the number because further the multiples will be greater than the number itself.
    for(i = 1 ; i <= (num/2) ; i++)
    {
        int rem = num%i;

        if(rem == 0)
            sum = sum + i;
    }

        if(num == sum)
            cout<<"You entered a perfect number\n";

        else
            cout<<"Not perfect number\n";

}

//main
int main(){

int number, sum = 0, rem, i;

cout<<"Enter number:\n";
cin>>number;

//function call
check_perfect_number(number);

return 0;

}


/*

Test cases:
1. Input : Enter any number: 6
   Output : You entered a perfect number


2.Input:  Enter any number: 15
  Output: Not perfect number

Time complexity: O(n)
Space Complexity : O(1)

*/