How to output fraction instead of decimal number?

In C++, When I calculate 2/3, it will output decimal values, how can I just get the original format (i.e.g 2/3) instead of 0.66666667

Thanks

Solution 1:

You can't. You would need to write a class dedicated to holding rational numbers (i.e. fractions). Or maybe just use the Boost Rational Number library.

Solution 2:

If I understand correctly, you have a floating point number (a float or double type variable), and you'd like to output this value as a fraction.

If that is the case, you need to further specify your question:

• A FP number is a fraction, by definition: A FP number consists of two integers, a mantissa m and an expontent e (and a sign, but that's irrelevant here). So each FP number is really a pair (m,e), and the value f it represents is f=mb^e (where b is a fixed integral base, usually 2). So the natural representation as a fraction is simply m / b^(-e) with e<0 (if e>=0 , f is integral anyway).
• However, you probably want to get the fraction with the smallest reasonable divisor. This is a different question. To get is, you could e.g. use the bestappr function from the Pari/GP library. In your case, you'd probably use bestappr(x, A), with x your input, and A the largest denominator you want to try. bestappr will give you the fraction closest to x whose denominator is still smaller than A.

Solution 3:

write your own Rational class to calculate divisions

class Rational
{
public:
    int numerator, denominator;

    Rational(int num, int den=1){
        numerator = num;
        denominator=den;
    }
    Rational(Rational other){
        numerator = other.numerator;
        denominator = other.denominator;
    }
    double operator / (int divisor){
            denominator *= divisor;
            simplificate();
            return getrealformat();
    }
    Rational& operator / (int divisor){
            denominator *= divisor;
            simplificate();
            return this;
    }
    Rational& operator / (Rational &divisor){
            numerator *= divisor.numerator;
            denominator *= divisor.denominator;
            simplificate();
            return this;
    }
    double operator / (int divisor){
            denominator *= divisor;
            simplificate();
        return getrealformat();
    }
    double getrealformat(){
        return numerator/denominator;
    }
    simplificate(){
        int commondivisor = 1;
        for(int i=2;i<=min(abs(numerator), abs(denominator));i++)
            if( numerator%i == 0 && denominator%i == 0 )
                commondivisor = i;
        numerator /= commondivisor;
        denominator /= commondivisor;
    }
};

use

Rational r1(45), r2(90), r3=r1/r2;
cout<<r3.numerator<<'/'<<r3.denominator;
cout<<r3.getrealformat();

Solution 4:

how can I just get the original format (i.e.g 2/3) instead of 0.66666667

Only with great difficulty by wrapping something like the GMP library with custom output operators. Below is a bit more on GMP:

What is GMP?

GMP is a free library for arbitrary precision arithmetic, operating on signed integers, rational numbers, and floating point numbers. There is no practical limit to the precision except the ones implied by the available memory in the machine GMP runs on. GMP has a rich set of functions, and the functions have a regular interface.

The main target applications for GMP are cryptography applications and research, Internet security applications, algebra systems, computational algebra research, etc.

GMP is carefully designed to be as fast as possible, both for small operands and for huge operands. The speed is achieved by using fullwords as the basic arithmetic type, by using fast algorithms, with highly optimised assembly code for the most common inner loops for a lot of CPUs, and by a general emphasis on speed.

GMP is faster than any other bignum library. The advantage for GMP increases with the operand sizes for many operations, since GMP uses asymptotically faster algorithms.

The first GMP release was made in 1991. It is continually developed and maintained, with a new release about once a year.