# C program to find perfect numbers between 1 to n

Write a C program to find all Perfect numbers between 1 to n. C program to find all perfect numbers between given range. How to generate all perfect numbers between given interval using loop in C programming. Logic to find all perfect numbers in a given range in C programming.

Example

Input

`Input upper limit: 100`

Output

`Perfect numbers between 1 to 100: 6, 28`

## Required knowledge

Must know – Program to check divisibility.

### What is Perfect number?

Perfect number is a positive integer which is equal to the sum of its proper positive divisors.

For example: 6 is the first perfect number
Proper divisors of 6 are 1, 2, 3
Sum of its proper divisors = 1 + 2 + 3 = 6.
Hence 6 is a perfect number.

## Logic to find all Perfect number between 1 to n

Step by step descriptive logic to find Perfect numbers from 1 to n.

1. Input upper limit from user to find Perfect numbers. Store it in a variable say end.
2. Run a loop from 1 to end, increment 1 in each iteration. The loop structure should look like `for(i=1; i<=end; i++)`.
3. For each iteration inside loop print the value of i if it is a Perfect number.

## Program to find all perfect numbers between 1 to n

``````/**
* C program to print all Perfect numbers between 1 to n
*/

#include <stdio.h>

int main()
{
int i, j, end, sum;

/* Input upper limit to print perfect number */
printf("Enter upper limit: ");
scanf("%d", &end);

printf("All Perfect numbers between 1 to %d:\n", end);

/* Iterate from 1 to end */
for(i=1; i<=end; i++)
{
sum = 0;

/* Check whether the current number i is Perfect number or not */
for(j=1; j<i; j++)
{
if(i % j == 0)
{
sum += j;
}
}

/* If the current number i is Perfect number */
if(sum == i)
{
printf("%d, ", i);
}
}

return 0;
}``````

Once, you got the logic to print perfect numbers from 1 to n. You can easily modify the logic to print perfect numbers in given range. I am writing the below program with little modification to print perfect numbers in given range.

## Program to generate perfect numbers in given range

``````/**
* C program to print all Perfect numbers between 1 to n
*/

#include <stdio.h>

int main()
{
int i, j, start, end, sum;

/* Input lower and upper limit from user */
printf("Enter lower limit: ");
scanf("%d", &start);
printf("Enter upper limit: ");
scanf("%d", &end);

printf("All Perfect numbers between %d to %d:\n", start, end);

/* Iterate from start to end */
for(i=start; i<=end; i++)
{
sum = 0;

/* Check whether the current number i is Perfect number or not */
for(j=1; j<i; j++)
{
if(i % j == 0)
{
sum += j;
}
}

/* If the current number i is Perfect number */
if(sum == i)
{
printf("%d, ", i);
}
}

return 0;
}``````

Output

```Enter lower limit: 1
Enter upper limit: 1000
All Perfect numbers between 1 to 1000:
6, 28, 496,```

Happy coding 😉

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