C++, issues converting decimal to fraction

[andrew222]

Hi all,

I am working on a C++ program that converts a decimal to a fraction, finds the lowest common multiple, multiplies the numerator by the denominator, then reduces the fraction again so the fraction will be 'numerator/1'.

I am using this code in a larger program to change a floating point slope value to a whole value for slope-intercept equations and standard form equations.

The program will run but I tested almost 500 numbers and 20 numbers made the program crash (it stalled and did not finish the equation, I had to close the terminal and open it up again... )

These 20 numbers I had problems with:

2.36, 7.36, 1.11, 1.001, 1.66, 1.88, 2.22, 2.13, 3.24, 3,26, 3.32, 3.43, 3.49, 3.51, 3.57, 3.68, 3.74, 3.76, 3.82

(I am sure there are more...)

I have tried c-style casting and dynamic and static casting to try to resolve this issue. Can someone help me out and point out why these certain numbers make the program crash and offer a possible sloution?

I tried debugging this program on gdb and keep on getting this frustrating message..

(gdb) break 16
No line 16 in file "init.c".
(gdb)


Here is the program's code, I also attached the tarball of the code to this thread as well:

//example.cc
#include <iostream>
#include "reduce.h"
#include "decimal-to-fraction.h"
using namespace std;

int main()
{
	double deci;
	double n, d;

	while(1) {
		cout << "Enter a decimal to convert to a fraction ('0' to quit): ";
		cin >> deci;
		cin.ignore(INT_MAX, '\n');
		if(!deci) exit(0);
		
		dec_to_frac(deci, n, d);
		
		if (n * d != n){
			cout << '\n' << deci << " = " << n << '/' << d << "\n\n";
			cout<<'\n' << d << " x " << n;
			n = d * n;
			cout<< " = " << n << "\n\n";
			cout<<'\n' << n << '/' << d; 
			reduce(n, d);
		
			cout << " = " << n << '/' << d << "\n\n";

			cout<<'\n' << n << "\n\n";
		}
		
		else
			cout<<'\n' << deci<< "\n\n";
	
	}

	return 0;
}

#ifndef _REDUCE_H_

#error You must include "reduce.h" before this file

#endif /* def _REDUCE_H_ */



#ifndef _DECIMAL_TO_FRACTION_H_

#define _DECIMAL_TO_FRACTION_H_



void dec_to_frac(double decimal, double &numerator, double &denominator)

{

	//numerator = static_cast<int >(decimal);
	//numerator = (int )decimal;
	numerator = decimal;

	denominator = 1;
	


	while(numerator != (int)numerator) {

		numerator *= 10;

		denominator *= 10;

	}

	reduce(numerator, denominator);

}



#endif /* def _DECIMAL_TO_FRACTION_H_ */

#ifndef _REDUCE_H_

#define _REDUCE_H_



void reduce(double &numer, double &denom)

{

	int i;



	for(i=2; i<=numer; ++i) {
		

		if( ((numer/i) == ((int )(numer/i))) && ((denom/i) == ((int)(denom/i))) ) {

			numer /= i;

			denom /= i;

			--i;              

		}

	}

}



#endif /* def _REDUCE_H_ */

[Cabhan]

Add in some cerr outputs so that you can track where in the program it gets. Make sure to add some to the loops and print out the numbers it's working with.

[andrew222]

Thank you Cabhan, I will look up Cerr outputs in some of my books.