Calculating non-integer exponents in iOS

Question

I've been working on my math parser a bit, and I have come to realize that a bit of code I'm using is unable to handle an exponent that is non-interger. The bit of code I'm using seems to work just fine with an int, but not with a double.

else if ([[token stringValue] isEqualToString: @"^"])
    {
        NSLog(@"^");
        double exponate = [[self popOperand] intValue];
        double base     = [[self popOperand] doubleValue];
        result = base;
        exponate--;
        while (exponate)
        {
            result *= base;
            exponate--;
        }
        [self.operandStack addObject:  [NSNumber numberWithDouble: result]];

    }

' Using Objective-C, how do I make something like 5^5.5 evaluate properly? (6987.71242969)

Answer 1

Let library code do the work for you:

double exponent = [[self popOperand] doubleValue];
double base = [[self popOperand] doubleValue];

[self.operandStack addObject:@(pow(base, exponent))];