C program error - outputting 0

Question

I have been trying to get this to work for days now and I still cannot figure out the error. When I output the code, it prints, but it will not find the amicable pairs (divisor of first == second, and vice versa).

#include <stdio.h>
#include <stdlib.h>
#define _USE_MATH_DEFINES
#include <math.h>

int sumDivisors( int num );

int sumDivisors( int num )
{
  int counter, total;
  for( counter = 1; counter < num; counter++ )
    {
      if( num % counter == 0 )
        {
          total += counter;
        }
    }
  return ( total );
}

int main( void )
{
  int higher, lower, lowx, lowy, x, y, numOfPairs = 0;

  printf( "This program finds all amicable numbers within a range. \n" );
  printf( "Please enter a lower limit: \n" );
  scanf( "%d", &lower );
  printf( "Please enter a higher limit: \n" );
  scanf( "%d", &higher );


  for( lowx = lower; lowx <= higher; lowx++ )
    {
      for( lowy = lower; lowy <= higher; lowy++ )
        {
          if( sumDivisors( lowx ) == sumDivisors( lowy ) )
            {
              numOfPairs++;
              printf( "Pair #%d: (%d, %d)\n", numOfPairs, lowx, lowy );
            }
        }
    }

  printf( "There are %d amicable pairs from %d to %d\n", numOfPairs, lower, higher );
  system("pause");
  return ( 0 );
}

Consider writing the inner loop as for( lowy = lowx + 1; lowy <= higher; lowy++ ) to avoid repetitions. — Bob__
– Bob__, Commented Sep 20, 2016 at 22:04
On further thinking, you may have misinterpret the definition of amicable numbers, which are two different numbers so related that the sum of the proper divisors of each is equal to the other number. You can find a list of the first pairs at OEIS - A063990. Look at this Q&A for a more interesting optimization. — Bob__
– Bob__, Commented Sep 21, 2016 at 11:39
Yah, that was a logical error. I changed if( sumDivisors( lowx ) == sumDivisors( lowy ) ) to if( sumDivisors( lowx ) == lowy && if( sumDivisors( lowy ) == lowx), and that worked — Submersed24
– Submersed24, Commented Sep 22, 2016 at 12:02

Masked Man · Accepted Answer · 2016-09-20 21:54:17Z

6

You are not assigning any value to total in your code:

int sumDivisors( int num )
{
  int counter, total;
  for( counter = 1; counter < num; counter++ )
    {
      if( num % counter == 0 )
        {
            total += counter;
        }
    }
  return ( total );
}

so it contains garbage not predictable value!

it should be like: int counter, total = 0;

answered Sep 20, 2016 at 21:54

Masked Man

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4 Comments

Submersed24 Over a year ago

Oh gosh... thank you... you saved me. I am used to null being zero

Stack Exchange Broke The Law Over a year ago

@Submersed24 What does it have to do with null being zero?

Submersed24 Over a year ago

I used to think variables are defaulted at 0, so you don't need to set them to zero

Masked Man Over a year ago

@Submersed24, I'm glad that it helped! :)

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