Problem with reading from file causing infinite loop

Question

Ok this program I am working on seems to be all ok except there is a problem. Here is the code

#include <iostream>
#include <fstream>

using namespace std;

/*
Function Name: CalculateBinary
CalculateBinary takes a number from the main function and finds its binary form.
*/

void CalculateBinary( long InputNum)
{   
    //Takes InputNum and divides it down to "1" or "0" so that it can be put in binary form.
    if ( InputNum != 1 && InputNum != 0)
        CalculateBinary(InputNum/2);

    // If the number has no remainder it outputs a "0". Otherwise it outputs a "1". 
    if (InputNum % 2 == 0)
        cout << "0";
    else
        cout << "1";
}


void main()
{
    // Where the current number will be stored
      long InputNum;

    //Opens the text file and inputs first number into InputNum. 
    ifstream fin("binin.txt");
    fin >> InputNum;

    // While Input number is not 0 the loop will continue to evaluate, getting a new number each time.
    while (InputNum >= 0)
    {
        if(InputNum > 1000000000)
            cout << "Number too large for this program ....";
        else
            CalculateBinary(InputNum);

        cout << endl;
        fin >> InputNum;        
    }
}

Here is the text file I am reading in

When I get to 8764, it just keeps reading in this number over and over again. It ignores the 2147483648. I know I can solve this by declaring InputNum as a long long. But I want to know why is it doing this?

Looks familiar: stackoverflow.com/questions/7397034/infinite-loop-problem — Mysticial
– Mysticial, Commented Sep 13, 2011 at 17:01
depending on the input from binin.txt this program may have UB. — wilhelmtell
– wilhelmtell, Commented Sep 13, 2011 at 17:01
@Mystical it is the same thing, but I didnt quite ask what I wanted to in that question — Steffan Harris
– Steffan Harris, Commented Sep 13, 2011 at 17:05

Sarfaraz Nawaz · Accepted Answer · 2011-09-13 17:03:30Z

4

That is the usual problem with such loops which you've written.

The correct and the idiomatic loop is this:

ifstream fin("binin.txt");
long InputNum;
while (fin >> InputNum && InputNum >= 0)
{
   //now construct the logic accordingly!
    if(InputNum > 1000000000)
         cout << "Number too large for this program ....";
    else
         CalculateBinary(InputNum);
    cout << endl;
}

answered Sep 13, 2011 at 17:03

Sarfaraz Nawaz

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2 Comments

Sarfaraz Nawaz Over a year ago

@pezcode: There was a typo. I wanted to initialize InputNum with 0.

MSN Over a year ago

@Nawaz, just reverse the while loop condition.

Puppy · Accepted Answer · 2011-09-13 17:02:11Z

2

That number is too large for a long to store, so fin >> InputNum; does nothing. You should always read as while(fin >> InputNum) { ... }, as that will terminate the loop immediately on failure, or at least check the stream state.

answered Sep 13, 2011 at 17:02

Puppy

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Comments

NPE · Accepted Answer · 2011-09-13 17:00:45Z

0

It would appear that the long type on your platform is 32 bits wide. The number 2147483648 (0x80000000) is simply too large to be represented as a signed 32-bit integer. You either need an unsigned type (which obviously won't work with negative numbers) or a 64-bit integer.

Also, you should check whether the read is successful:

  ...
  cout << endl;
  if (!(fin >> InputNum)) break; // break or otherwise handle the error condition
}

answered Sep 13, 2011 at 17:00

NPE

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Comments

user405725 · Accepted Answer · 2011-09-13 17:01:46Z

0

You don't check for EOF, thus being trapped in a loop forever. fin >> InputNum expression returns true if succeeded, false otherwise, so changing you code to something like this will solve the problem:

while ((fin >> InputNum) && InputNum >= 0)
{
  // ...
}

answered Sep 13, 2011 at 17:01

user405725

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