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

Basic C programming, If statement, For loop, Nested loop

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.

- Input upper limit from user to find Perfect numbers. Store it in a variable say
`end`. - Run a loop from 1 to
`end`, increment 1 in each iteration. The loop structure should look like`for(i=1; i<=end; i++)`

. - 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 😉