Fraction Help

[tivanenk]

I need to write a program, but ran into a problem. My teacher didn't teach us how to substract/divide/multiply/add fractions. Can anybody help me? I need some help in this.

[DtY]

You mean from a math perspective? This is... grade five math?

Multiplying fractions a/b * c/d = (a*c)/(b*d)
Dividing is multiplying by the inverse of the second: (a/b)/(c/d) / (a*d)/(b*c)

Adding is done by adding the numerators once a common denominator is found. Subtraction is the same as adding the negative of the second.

[Coldkick]

Maybe he means he wants to calculate but is getting an error because it is the wrong type.
Two ways to fix this.
Change the variable type to real OR put round () around the equations. Some times integers are required, thus you must use the latter (for graphics etc).

[tivanenk]

actually, the help I need is the teacher told me that Turing will HAVE to output a fraction as an answer, but mine outputs the decimal
here is the formula I use:

var ra : real
var rb : real
var rc : real
var rd : real
var re : real
get ra
get rb
get rc
get rd
re := ((ra*rc)/(rb*rd))
put re

[DtY]

re := ((ra*rc)/(rb*rd))

/ is division, when I used it in my post, I was meaning a literal slash (or fraction bar).

[tivanenk]

I understand, but I still don't understand how to add fractions so the answer will BE a fraction

[TerranceN]

I think DtY means something like this:

Turing:

var a : int := 3 var b : int := 5 put (intstr(a) + " / " + intstr(b) + " = " + realstr(a/b, 2))

Since Turing will automatically evaluate any fractions you type, you have to manually make it look like a fraction by outputting a "/".

[tivanenk]

that's better, by I need to make it so you can input ANY fraction, it is like an equation.
Example:
a/b + c/d = e/f
You can replace a, b, c, d with anything

[DtY]

You have to store the numerator and denominator separately, then when you want to output it you would output numerator "/" denominator (where the slash is a literal slash (or fraction bar) and not the division operator).

You would have separate formulae for the numerator and denominator. The multiplication and division are easy enough, I listed them up there. If you're not sure about addition or subtraction, find a piece of paper and try it using variables, that will give you a generic formula for rational addition.

After you do that you will probably want to reduce the fraction (if you dread this, ask your teacher if it's necessary, it might not be if you're in a lower grade CS class), if you do the most efficient way of finding the greatest common divisor is the equation gcd(a,b) = gcd(b, a mod b). More on that on Wikipedia.

[tivanenk]

ok, thanks!