Write a C program to print 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 program.

**Example**

**Input**

Input upper limit: 100

**Output**

Perfect numbers between 1 to 100: 6, 28

## Required knowledge

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

Must have programming knowledge for this program.

## What is Perfect number?

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

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

Below is the step by step descriptive logic to find Perfect numbers from 1 to n.

- Read upper limit from user to print all Perfect numbers. Store it in some variable say end.
- Run a loop from 1 to end, incrementing 1 in each iteration. The loop structure should look like for(i=1; i<=end; i++). Inside this loop, you need to check each element for Perfect number.
- Inside the loop print the current number 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; /* Read 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; /* Read 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; }

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

Happy coding ;)

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