Perfect Number Program in C

Perfect Number

In mathematics, a perfect number is a positive integer that is equal to the sum of its positive divisors, excluding the number itself.

For example, 6 is a positive number that is completely divisible by 1, 2, and 3. We know that the number is also divisible by itself but we will include it in the addition of divisors. When we add these divisors (1 + 2 + 3 = 6), it produces 6, which is equal to the number that we have considered. So, we can say that 6 is a perfect number.

There are two ways to find the perfect number:

Using for Loop
Using while Loop

Using for Loop

Write a C program that accepts an input from the user and checks the given number is a perfect or not.

/*C program to check whether the given number is the Perfect number*/
#include<stdio.h>
#include<conio.h>
void main()
{
// declare and initialize the variables
int num, rem, sum = 0, i;
// take an input from the user.
printf("Enter a number\n");
scanf("%d", &num);    
// find all divisors and add them
for(i = 1; i < num; i++)
                     {
                              rem = num % i;
                             if (rem == 0)
                                        {
                                               sum = sum + i;
                                         }
                        }
if (sum == num)
                      printf(" %d is a Perfect Number");
           else
                      printf("\n %d is not a Perfect Number");
getch();
}

Output

In the above output, the loop condition is validated at each iteration and counter i is incremented by 1. Inside the loop, various operations are performed such as:

Step 1: i = 1, rem = num % i, => 28 % 1 = 0. Here rem = 0.

Step 2: rem == 0, condition true.

Step 3: sum = 0 + i, sum = 0 + 1 => 1

// i is incremented by 1

Step 4: i = 2, rem = num % i, => 28 % 2 = 0. Here rem != 0, Condition is true;

Sum = 1 + i => 1 +2 = 3

Step 5: i = 3, rem = num % i, => 28 % 3 = 1. Here rem = 0, Condition is false;

Step 6: i = 4, rem = num % i, => 28 % 4 = 0. Here rem == 0, Condition is true;

Sum = 1 + i => 3 + 4 = 7

Similarly, check all condition;

Step 7: Sum == num, 28 == 28, Print the message "Entered number is a Perfect Number"

Using while Loop

Example 2: Let's create a C Program to find the perfect number using a while loop.

/*Create a C Program to find the perfect number using while loop*/
#include<stdio.h>
#include<conio.h>
void main()
{
int i = 1, num, Sum = 0;
printf(" Enter any number to check Perfect Number \n");
scanf("%d", &num);

while(i < num )
                     {
                               if(num % i == 0)
                               Sum = Sum + i;
                               i++;
                     }
           if(Sum == num)
                  printf("\n %d is Perfect Number", num);
           else
           printf("\n %d is not a Perfect Number", num);
getch();
} 

Output

Example 3: Find the perfect number between two numbers through a C program.

#include<stdio.h>
#include<conio.h>
void main()
{
int num, Sum = 0, i, Max, Min;
// Take two number from the user: min and max
printf("Enter the minimum and the maximum value\n");
scanf("%d %d", &Min, &Max);

printf("\n Perfect Number between %d and %d are\n ", Min, Max);
for(num = Min; num <= Max; num++)
                     {
                             for(i = 1, Sum = 0; i < num; i++)
                                     {
                                            if(num %i == 0)
                                            Sum = Sum + i;
                                      }
                              if(Sum == num)
                             printf("%d \t", num);
                      }
  getch();
}

Output