Converting Decimal to C ++ Fraction

Question

What is an algorithm that I can use to convert and enter a decimal number into fractional form in C ++. For example, if I enter 1.25, I would like the conversion to output to be 1 1/4.

Answer 1

First get the fractional part, and then take gcd. Use the Euclidean algorithm http://en.wikipedia.org/wiki/Euclidean_algorithm

void foo(double input)
{
    double integral = std::floor(input);
    double frac = input - integral;

    const long precision = 1000000000; // This is the accuracy.

    long gcd_ = gcd(round(frac * precision), precision);

    long denominator = precision / gcd_;
    long numerator = round(frac * precision) / gcd_;

    std::cout << integral << " + ";
    std::cout << numerator << " / " << denominator << std::endl;
}

long gcd(long a, long b)
{
    if (a == 0)
        return b;
    else if (b == 0)
        return a;

    if (a < b)
        return gcd(a, b % a);
    else
        return gcd(b, a % b);
}

Answer 2

I came up with an algorithm for this problem, but I think it is too long and can be executed with fewer lines of code. Sorry for the poor indentation, it is trying hard to align everything with overflow.

#include <iostream>
using namespace std;


// converts the string half of the inputed decimal number into numerical values void converting
 (string decimalNumber, float&numerator, float& denominator )

 { float number; string valueAfterPoint =decimalNumber.substr(decimalNumber.find("."    ((decimalNumber.length() -1) )); // store the value after the decimal into a valueAfterPoint 

int length = valueAfterPoint.length(); //stores the length of the value after the decimal point into length 

numerator = atof(valueAfterPoint.c_str()); // converts the string type decimal number into a float value and stores it into the numerator

// loop increases the decimal value of the numerator by multiples of ten as long as the length is above zero of the decimal

for (; length > 0; length--)  
    numerator *= 10;

do
 denominator *=10;
  while  (denominator < numerator);



// simplifies the the converted values of the numerator and denominator into simpler values for          an easier to read output 


void simplifying (float& numerator, float& denominator) { int maximumNumber = 9; //Numbers in the tenths place can only range from zero to nine so the maximum number for a position in a position for the decimal number will be nine

bool isDivisble; // is used as a checker to verify whether the value of the numerator has the       found the dividing number that will a value of zero
 // Will check to see if the numerator divided denominator is will equal to zero


   if(int(numerator) % int(denominator) == 0) {
   numerator /= denominator;
   denominator = 1;   
   return; }


  //check to see if the maximum number is greater than the denominator to simplify to lowest     form while (maximumNumber < denominator) { maximumNumber *=10;  }


 // the maximum number loops from nine to zero. This conditions stops if the function isDivisible is true 
 for(; maximumNumber > 0;maximumNumber --){

 isDivisble = ((int(numerator) % maximumNumber == 0) && int(denominator)% maximumNumber == 0);

  if(isDivisble)
 {
    numerator /= maximumNumber;  // when is divisible true numerator be devided by the max        number value for example 25/5 = numerator = 5

   denominator /= maximumNumber; //// when is divisible true denominator be devided by themax        number value for example 100/5 = denominator = 20

 }


 // stop value if numerator and denominator is lower than 17 than it is at the lowest value
 int stop = numerator + denominator;

 if (stop < 17)
 {
     return;
 } } }