Question

i am new to objective C and I started to learn the basics in iOS development.

How can I easily calculate with fractions in Objective C?

Example 1: 1/8000 * 60

Example 2: 1/640 / 1/400

I need to have the result (if its < 1) as a fraction, too.

Answer 1

I think I would implement a new class, say Fraction which has two properties, the numerator and denominator. I would then implement four (or more if necessary) of the following functions:

- (Fraction*) add:(Fraction*)operand;
- (Fraction*) subtract:(Fraction*)operand;
- (Fraction*) multiply:(Fraction*)operand;
- (Fraction*) divide:(Fraction*)operand;
- (Fraction*) invert;
+ (Fraction*) fractionByAdding:(Fraction*)op1 to:(Fraction*)op2;
+ (Fraction*) fractionBySubtracting:(Fraction*)op1 from:(Fraction*)op2;
+ (Fraction*) fractionByMultiplying:(Fraction*)op1 with:(Fraction*)op2;
+ (Fraction*) fractionByDuviding:(Fraction*)op1 by:(Fraction*)op2;
+ (Fraction*) fractionByInverting:(Fraction*)operand;

In these methods, do the usual arithmetic you learned in school. Remember to simplify if both numerator and denominator has common divisors.

EDIT: Example implementation for one of these functions:

- (Fraction*) add:(Fraction*)operand {
    return [Fraction fractionByAdding:self to:operand];
}

+ (Fraction*) fractionByAdding:(Fraction*)op1 to:(Fraction*)op2 {
    int num = (op1.numerator * op2.denominator) + (op2.numerator * op1.denominator);
    int denom = op1.denominator * op2.denominator;
    return [[Fraction alloc] initWithNumerator:num andDenominator:denom];
}

Optionally you could add a reduce or simplify method and possibly an allowReducible property and an isIrreducible method. You could also implement isEqual and compareTo methods. A description should just print “a/b” as an NSString.