Perfect numbers between 1 and 1000

Question

I don't understand why this program doesn't give any output. I just can't see the bug. This is a program to find every perfect number between 1 and 1000. Please help me find the bug. Thanks.

#include <stdio.h>

int main(){
    int number=1, i, sum=0;

    while(number<=1000){

        for(i=1; i<number; i++){
            if(number%i==0){
                sum+=i;
            }
        }

        if(sum==number){
            printf("%d is perfect\n", numero);
        }
        number++;
    }

    return 0;   
}

@mch But that outputs 6, 28, and 496. [I don't get it](http://rextester.com/VSFVE45383). — Tim Biegeleisen, Aug 22 '18 at 08:20
@TimBiegeleisen that's the correct output: https://en.wikipedia.org/wiki/List_of_perfect_numbers — mch, Aug 22 '18 at 08:22
@user you might want to include a definition for what is a perfect number, just to make your question complete. — Tim Biegeleisen, Aug 22 '18 at 08:23
If you try printing an else along with the sum and number, this might have helped you spot the problem. — doctorlove, Aug 22 '18 at 08:24
Set sum = 0 before for loop and change numero to number, you can check on [Perfect Number](http://c.net-question.in/c-basic-programs/perfect-numbers-between-1-and-100) — Hiren Patel, Aug 22 '18 at 08:38

Laurent H. · Accepted Answer · 2018-08-22T08:44:52.583

As already said, you have to reset the sum to zero at the beginning of the loop.
You also have to replace numero with number (typo).
And to go further, I suggest you to use a for loop instead the while loop, which I find more readable IMHO. The inner for loop can also stop when i <= number/2 to optimize a bit. Here is my suggestion of code:

#include <stdio.h>

int main(){

    int sum;

    for(int number = 1;number <= 1000; number++){
        sum = 0;

        for (int i = 1; i <= number/2; i++){
            if (number % i == 0){
                sum += i;
            }
        }

        if (sum == number){
            printf("%d is perfect\n", number);
        }
    }

    return 0;
}

Output:

6 is perfect
28 is perfect
496 is perfect

score 0 · Answer 2 · answered Aug 22 '18 at 08:24

You did not reset the sum in the loop:

#include <stdio.h>

int main(){
    int number=1;

    while(number<=1000){
        int i, sum=0;

        for(i=1; i<number; i++){
            if(number%i==0){
                sum+=i;
            }
        }

        if(sum==number){
            printf("%d is perfect\n", numero);
        }
        number++;
    }

    return 0;

}

for the record, according to Wikipedia:

In number theory, a perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself (also known as its aliquot sum). Equivalently, a perfect number is a number that is half the sum of all of its positive divisors (including itself) i.e. σ1(n) = 2n.

Çağatay Yücelen · Answer 3 · 2018-08-22T08:47:34.987

0

There are 3 perfect numbers between 1 and 1000.

{6, 28, 496}

Your code is mostly correct but you forgot to reset the sum value after each loop iteration.

 ...
    }
    number++;
    sum = 0; // set sum to zero at the end of the while loop
  }

And also you misspelled the number variable as numero inside printf function.

printf("%d is perfect\n", numero);

edited Aug 22 '18 at 08:47

answered Aug 22 '18 at 08:32

Çağatay Yücelen

3
2

score 0 · Answer 4 · answered Aug 22 '18 at 08:59

#include <stdio.h>

int main(){

    int number = 1, sum = 0;

    while(number<=1000){

        sum = 0;
        for(int i = 1; i < number; i++){

            if(number % i == 0){
                sum += i;
            }
        }

        if(sum == number){
            printf("%d is perfect\n", number);
        }
        number++;
    }
    return 0;
}

reset the value of sum to 0 and change numero to number in printf

Perfect numbers between 1 and 1000

4 Answers4