Using Instance Variables in Functions [duplicate]

So, this might be a really simple question and if it's obvious, I'd like to apologise now but I couldn't find answers to it anywhere. So, here it is. Supposing I have a class:

@interface MyClass : NSObject

@property int Radius;
@property int Iterations;
@property UInt32 * Data;

@end

and in my implementation file I have:

@interface MyClass()

void Foo(int * newData);

@end

@implementation MyClass

// Synthesize block
// Getter-Setter block

void Foo(int *newData) {
    // Do some stuff
    _Iterations++;                   // Use of undeclared identifier _Iterations
    Iterations++;                    // Use of undeclared identifier Iterations
    self.Iterations++;               // Use of undeclared identifier self
}

@end

Could someone explain why I'm having this error and how I should go about fixing it?

Thanks,