C Exercises: Check whether a given number is a perfect number or not

C For Loop: Exercise-27 with Solution

Write a C program to check whether a given number is a 'Perfect' number or not.

A perfect number is a positive integer that is equal to the sum of its proper divisors, excluding itself. For example, the number 6 is a perfect number because its divisors are 1, 2, and 3, and the sum of these divisors is 6.

Visual Presentation:

Sample Solution:

C Code:

/* 
   Perfect number is a positive number which sum of all positive divisors excluding that number is equal to that number.
   For example, 6 is a perfect number since the divisors of 6 are 1, 2, and 3. Sum of its divisors is 1 + 2 + 3 = 6
*/

#include <stdio.h> // Include the standard input/output header file.

void  main()
{
  int n, i, sum; // Declare variables for user input, loop control, and sum.
  int mn, mx;    // Variables mn and mx are declared but not used. Consider removing them.

  printf("Input the  number : "); // Prompt the user for input.
  scanf("%d", &n); // Read the value of 'n' from the user.
  sum = 0; // Initialize the sum variable.

  printf("The positive divisors  : "); // Print a message to indicate positive divisors are being displayed.

  for (i = 1; i < n; i++) // Loop to find and display positive divisors.
  {
    if (n % i == 0) // If 'i' is a divisor of 'n'.
    {
      sum = sum + i; // Add 'i' to the sum.
      printf("%d  ", i); // Print 'i' as a positive divisor.
    }
  }

  printf("\nThe sum of the divisors is : %d", sum); // Print the sum of the divisors.

  if (sum == n) // Check if the sum of divisors is equal to the original number.
    printf("\nSo, the number is perfect."); // If true, print that the number is perfect.
  else
    printf("\nSo, the number is not perfect."); // If false, print that the number is not perfect.

  printf("\n"); // Print a new line for better formatting.
}

Output:

Input the number: 28
The positive divisors: 1 2 4 7 14
The sum of the divisors is: 28
So, the number is perfect.

Input the number: 10
The positive divisors: 1  2  5
The sum of the divisors is: 8
So, the number is not perfect.

Explanation:

• Header inclusion:
• #include <stdio.h>: Includes the standard input/output header file for using functions like printf and scanf.
• Main function:
• int main(): The main function where the program execution begins.
• Variable Declaration:
• int n, i, sum;: Declares three integer variables:
• n for storing the user's input number.
• i for loop control.
• sum for storing the sum of the divisors.
• User input:
• printf("Input the number: ");: Prompts the user to input a number.
• scanf("%d", &n);: Reads the input number from the user and stores it in the variable n.
• Initial sum:
• sum = 0;: Initializes the sum variable to zero.
• Print Divisors Message:
• printf("The positive divisors: ");: Prints a message indicating the start of the list of positive divisors.
• Finding Divisors:
• for (i = 1; i < n; i++): A loop that runs from 1 to n-1 to find all positive divisors of n.
• if (n % i == 0): Checks if i is a divisor of n (i.e., if n modulo i is 0).
• sum = sum + i;: Adds i to the sum if i is a divisor.
• printf("%d ", i);: Prints the divisor i.
• Print Sum of Divisors:
• printf("\nThe sum of the divisors is: %d", sum);: Prints the total sum of the divisors.
• Check Perfect Number:
• if (sum == n): Checks if the sum of the divisors equals the original number n.
• printf("\nSo, the number is perfect.\n");: If true, prints that the number is perfect.
• else printf("\nSo, the number is not perfect.\n");: If false, prints that the number is not perfect.
• Return Statement:
• return 0;: Returns 0 to indicate successful execution of the program.

Flowchart:

C Programming Code Editor:

Previous: Write a program in C to find the sum of the series 1 +11 + 111 + 1111 + .. n terms.
Next: Write a c program to find the perfect numbers within a given number of range.