Calculate a Ratio in C#

Question

I thought this would be simple, but searching Google didn't seem to help.

I'm basically trying to write a function which will return a ratio as a string (eg 4:3) when supplies with two integers (eg 800 and 600).

string GetRatio(Int A, Int B) {
    // Code I'm looking for
    return Ratio;
}

score 39 · Accepted Answer · edited Feb 25 '19 at 14:18

39

You can simplify fractions by dividing numerator and denominator by their GCD:

var gcd = GCD(A, B);
return string.Format("{0}:{1}", A / gcd, B / gcd)

And a very basic function for calculating the GCD, using the Euclidean algorithm:

static int GCD(int a, int b) {
    return b == 0 ? Math.Abs(a) : GCD(b, a % b);
}

edited Feb 25 '19 at 14:18

Lennart

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answered Feb 09 '09 at 12:01

Konrad Rudolph

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Syntax Error @ return b == 0 ? a : gcd(b, a % b); function gcd not defined – Aamir Feb 09 '09 at 12:35
Note that depending on what you expect to get out of it, this might need some fine-tuning for negative inputs. – fuglede May 09 '18 at 13:58
1

@fuglede True, though the results were always mathematically sound. That said, I’ve changed the code to more closely match common definitions of the GCD. – Konrad Rudolph May 09 '18 at 16:34
@Aamir its recursion so how can GCD not be defined ? – Haseeb Mir Jun 17 '20 at 17:10

Tomas Pajonk · Answer 2 · 2009-02-09T12:10:45.030

5

Are you basically trying to get the greatest common denominator - GCD for the two numbers and then dividing them by that and thus getting your string ?

I.e: 800 : 600 ; the greatest common denominator = 200 thus 4:3.

This would be able to deal with all integer numbers. Sorry for not sending the code, but I think that from this on it should be simple enough.

public int GCD(int a, int b)

{
    while (a != 0 && b != 0)
    {
         if (a > b)
            a %= b;
         else
            b %= a;
    }
     if (a == 0)
         return b;
     else
         return a;
}

// Using Konrad's code: 

var gcd = GCD(A, B);
return string.Format("{0}:{1}", A / gcd, B / gcd)

edited Feb 09 '09 at 12:10

answered Feb 09 '09 at 12:01

Tomas Pajonk

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This site isn't for premade code, GateKiller. Take the knowledge you get from answers, write code. – Serafina Brocious Feb 09 '09 at 12:07
@Cody Brocious: Please can you direct me to the rules which state you cannot ask for code? – GateKiller Feb 09 '09 at 12:27
There are no rules saying you can't ask for code. But the whole purpose is to give people a knowledge base where they can find answers to problems. Just code snippets rarely explains everything about the solution and about the problem. – Filip Ekberg Feb 09 '09 at 12:33
Filip++ I couldn't agree more. Give a man a fish and all that. – Serafina Brocious Feb 09 '09 at 12:38
So is this where Gatekiller's hatred of 'plzsendtehcodez', came from? :-) – George Stocker Feb 14 '09 at 04:40

score 3 · Answer 3 · answered Feb 09 '09 at 12:23

Having played with such things in the past, I'll just add that dealing with signed values can get ugly. Let me suggest that the simplest way to handle signed values is to apply Konrad's approach to the absolute values of your original numbers, then prepend a '-' to the resulting string if the original values have different signs.

Using this approach, the Greatest Common Divisor of -100 and -35 is 5, for a ratio of 20:7. If the original inputs had been either of the pairs (-100 and 35) or (100 and -35), you'd still get a GCD of 5, and an initial result of 20:7, but the final answer would be -20:7 (i.e. standardized form regardless of which input was negative, just as both -6/2 and 6/-2 = -3).

score 0 · Answer 4 · answered Feb 09 '09 at 12:10

Other commentators have given good solutions for integers; if you really have to deal with floating-point values, though, you'll need something else. In general, two real numbers won't have a clean ratio that can be prettily printed; what you want is the closest rational approximation. Probably the best way to go about finding that is just to compute the continued fraction expansion of the quotient; Mark Dominus gives a good introduction to those on his blog.

score 0 · Answer 5 · answered Sep 26 '20 at 13:20

With Using following 2 functions, you will be able tow get ratio of two numbers without using division operations.

static int GCD(int p, int q)//find greatest common divisor
{
    if (q == 0)
    {
        return p;
    }

    int r = p % q;

    return GCD(q, r);
}
static string  FindRatio(int num1, int num2)
{

    string oran = "";
    int gcd;
    int quotient = 0;
    while (num1 >= num2)
    {
        num1 = num1 - num2;
        quotient++;
    }

    gcd = GCD(num1, num2);

    //without using division finding ration of num1 i1
    int i1 = 1;
    while (gcd*i1 != num1)
    {
        i1++;
    }
    //without using division finding ration of num1 i2
    int i2 = 1;
    while (gcd * i2 != num2)
    {
        i2++;
    }

    oran = string.Concat(quotient, " ", i1,"/",i2);
    return oran;
}

Output will be as follow:
coff num1 / num2

Calculate a Ratio in C#

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